Well, I'm not gonna tell you what I personally want or don't want. But I will tell you that, although they are very rare, such relationships do exist irl.
It's called ethical (consensual) non-monogamy (this is an umbrella term, which covers cuckqueaning as well as other things). For two people to be in such a relationship, they need to have an extraordinary amount of clear and open communication (which is the main difference between irl couples and the couples in stories). And they also tend to be extremely intelligent, because (and I'm just guessing here) in order to be in such a relationship, the couple needs to share an intellectual bond (or "intellectual intimacy"), which can be considerably stronger than any emotional or physical connection.
In fiction, there's going to be dialogue with tons of subtext, someone will cheat, and then the other party will realize they're into it, and they will jump into the deep end right away (for example).
In real life, these couples sit and talk for hours, go to couples therapy, establish all kinds of safe words and in a lot of cases, they will try it out one time and that's it (that is, if nobody chickens out beforehand).
I know this because a very dear friend of mine is in this kind of relationship (sort of). He hasn't slept with any women apart from his wife yet, but they are talking about it constantly, trying to figure out the boundaries and so on. And they 100% share that "intellectual bond" I was talking about earlier. Talking to the two of them is almost like talking to one person, they are literally in each other's heads.
To answer your other question, I personally don't think a relationship like that would fall apart if the male party wouldn't manage to find enough partners for himself (again, because of the intellectual bond such a couple normally shares)
And to answer your other other question, it's really not that difficult for a long-term married couple to find a woman to play with (regardless of their financial situation). Especially if they are being honest about everything right off the bat.
