open marriage

The addition of non-committal sex is indeed a welcome addition, when you can. Invested, committed sex also offers opportunities that I think are more meaningful as well. But - and no one can really be told this - it doesn't have much to do with the problem of your wife demonstrating that she's averse to you. When she's either separated from you or in an open marriage and boffing a new partner, it underlines the whole thing.

I saw a lot of people in the non-monogamy community and variants who approached it like a hobby. Together. So, imagine couple who like deep wilderness camping, or who are really into purebred dog shows - it's a thing with it's own culture to explore and community - something to join together with its own norms and practices. It's a thing outside of themselves that they both choose to join and do.  I've heard someone liken it to having a baby to save the marriage - something that requires extra rigour and intensity for both of them that gets them both looking ahead, side by side on an adventure, rather than staring each other down in a death spiral. That type often seemed to do it better and lasted for maybe 5-7 years most of the time before changing things up (closing the relationship, or switching the kink, or splitting).

The most successful are the ones who have a fetish of some kind for it - who genuinely find each others' participation (whether that is asynchronous or not), to be hot. So, if someone finds it hot to be chaste while their partner is not, or where one is a voyeur ... you get it. These tend to work really well with asynchronous desires. That doesn't seem to be either you or me, though I have participated as a guest in other relationships where that was the case for them.

What I learned after 3-4 years of this was that I enjoyed having sex, as I thought I would. 
I learned that I was attractive to women when I had thought I was the most unnattractive person on the planet,
I learned not not be so angry or ashamed at what were really modest needs that I know I would have settled for in my own relationship.
I learned, unequivocally, Empirically, that it was extremely important to my wife to not have sex with me - and that she did indeed have a robust sexual imagination that she wished to explore and would explore - but not with me.
I also learned that there was no end to her gaslighting - and that even with the data made plan and evident - that she would still insist our difference was that sex was "just more important to me than to her". She would never, ever, no matter how absurd her "sexual aversion" claim appeared - leave this behind.
I learned that she became jealous and abusive of me when I finally found a partner and did what she had been doing.
Her coping mechanism for the jealousy was to further isolate herself from me.
I learned that her "internal narrative" to give herself permission to do what she wanted, was so she could find her sexual spark elsewhere and then spend it with me.
She had no concept as to how contemptuous and disdainful that positions me in my role - as a plays for her to "spend" sexual energy and delight that she acquired with people she enjoys. Like they help her grin and bear it. Telling me this, repeatedly, thinking it was an positive example of how much work she was putting into the relationship to sustain it - where she was the hero in it - it really made me realize this was a bridge too far. She thought this was a positive comment.

Did it improve my marriage? No. In the long run not at all.
Did it end it? No - it was just another tableaux in which what had already been established was laid out in fine detail.
Regrets? Yes actually.

If I was to do over, I already had everything I needed to know laid out.
I did not have a mutual unique attraction with my wife - she might have loved me, and might have been a good mother to the kids, but did not love me as a wife loves a husband.
I wish I had put my energy into creating an amicable cooperative separation that retained all the things you want to enjoy about your marriage, with less rancour at being gaslighted and abused afterwards. 
I wish my eyes had been open during the early increase in sympatico and sex, to understand that she wasn't viewing intimacy with me as restorative.

There was nothing "marriage" was bringing to the table, that an amicable ex-spouse wasn't. We had no future as husband and wife. Co-parents maybe? An extended member of my family maybe. But not wife.

As such, it's not really a step toward some kind of invested marriage. It wasn't for me. It wasn't really for a lot of people I saw.
It had many positive elements - but those same elements could also be present and are now as a separated man. Those have little to do with my unrequited feelings for the person who was my wife (which thankfully have subsided and now I can see her like I might see a regular person - I don't think she'd last past too many dates with me these days)

Apocrypha and jerri ,
THANK YOU for this wealth of information! You provided good resources and I'm checking them out - even if it takes all day lol! Apocrypha I know some couples pursue open marriage as a fetish. I wish mine was that much fun! Yet I do feel like maybe my wife getting back into the habit of having sex is good for her. I have read that open marriage can help awaken dormant feelings - even if they are awkened by others - and maybe a give our marriage the kick it needs. If not then it's one more thing I tried and if everything fails at least I can say "I tried everything". At that point divorce really will be the last option on the table.

I reckon the best thing you've achieved here is that you have "done something" - and a pretty big something at that Brother sufferinhubby .
A big enough "something" (opening up the marriage) to fundamentally change the impasse of an ILIASM deal.

What you don't - yet - know is how this is all going to shake out for you (both) in the longer term.

But you have got it on the move, and that has to be a good thing.

The best thing out of this so far is that you firmly established your credibility.
You said you were going to open up the marriage, then you did exactly that.

So whatever you say next, your missus knows you mean it - and that is going to help enormously in bringing your ILIASM deal to resolution.

YES! That was exactly _precisely_ the rationale Mrs. Apocrypha provided to me, as her hypothesis that this might be the solution for her in "finding her libido" again. Awakening dormant feelings. "I finally felt sexual again! This is what you want of me, isn't it?" 

And when I agreed to it, I used exactly the rationale you did. It's likely someone tried to point out something to me that I'm going to drag you back to right now. I don't know that I would have listened then because I was so miserable I didn't think I had anything to lose. 

She WILL find her libido. Her libido is NOT the problem, even if she says it is, even if she THINKS it is.
It's having sex with YOU. It doesn't matter that you've studied the kama sutra forwards and backwards, or that you look like Jason Momoa. She doesn't see you as a viable sexual partner. She'll still likely treat you with absolute contempt or indifference if/when you eventually are able to find a partner a year or two from now. 

She'll find her libido - the same way as pretty much any newly separated person does, who thought herself sexually averse in her marriage. She'll explore it and enjoy it with other people. It doesn't have anything to do with you. It doesn't have anything to do with your marriage.   What do you think will happen for the marriage?

You DO have something to lose. You can learn to absolutely hate her through this, and given that you have children.
Given that it's already happening, that she's already having sex with someone who seems relatively new to your ecosystem -- and not with you, what's your criteria for "if it fails?"
For me, mine was "My wife and I do not increase the amount of intimacy we have for each other - to raise it to the threshold that I'd associate with a marriage."

You may start hearing about NRE. (New Relationship Energy)
I was in a pretty great triad in my mid twenties, but there was no internet to offer advice on doing it right.
My girlfriend's obsession with her new partner (who we met together as a couple and who became a good friend of mine) caused neglect of our relationship and we split off pretty soon. Leaving the two of them as a couple I was friends with.

COVID has possibly interfered with the NRE process and her attention may remain focused on this other fella for an extended period. In happier circumstances, the crazy dopamine rush of a new partner wears off, the partner reorients to all the components of her life and remembers her spouse (or his. NRE works for both) She may not have opportunity to become acclimated so the thrill will last an unusually long time.

Polyandry can happen, to be sure. Maybe less action with you than her fresh fella. Adding in a second lady will still be the right move. You may enjoy some NRE of your own, your wife may find your success attractive/sexy. You may rely on her less for companionship and the independence can also be attractive to a lady. 

I'd love to hear a second success story with polyamory having been the answer (Jerri's story being the example). 

I'm not sure I understand the direction you are going, based on what you said.
If you "don't mind the neglect from your wife" while she is with other people, then did you mind it before?
Do you regard the sexless marriage as a problem at all? Or, that there is a reason somewhere that you are sexless in this marriage, but it isn't shared?
If she doesn't want to have sex with you, and you don't mind that either... are you suggesting that the celibacy issue (at least with respect to her), is not really a problem in this case? If so, I apologize - I assumed you were trying to correct something that you felt was missing - but I may have just been projecting what I remember as my own situation.

It seems to me that what's developing between you is just her doing her own thing. I don't really see that much in what I used to recognize as an open marriage in the community, but your mileage may vary. Recognize and be ready for - if/when you jump into the same activity some years from now, that she may instantly react (as my wife did) as if you had cheated on her. She may instantly try to invoke a a divorce. Mine hit me. She'd been with someone, herself, for a year.

Sure, you have to give it your best try.
I guess, I'd want to be very clear on what you are trying - what problem are you trying to solve?