I'm not opposed to open relationships, and I'm not really a jealous person, but I also don't know what I'd get out of one. I don't want to actually have sex with that many people (fantasies are another matter), so I only see it becoming relevant once the passion starts to die down/the seven year itch kicks in, and maybe by then I'd feel committed enough due to a sense of shared history and stuff that I just don't even feel like opening that door, even if I think the risk is relatively small, because it seems like tacky or something (lol?). So in theory it's a maybe, but in practice it seems not all that likely.
Poly relationships I actually find harder to agree to. I think the idea that we can love lots of people is pretty optimistic. You hear it often enough from parents that when they have kids they feel such strong love for their children, then they look at their spouse and go "who are you, again?" Like the love they have for their kids only emphasizes how much of a 'stranger off the street' this person is that they built a life/home with, lol. So there's always going to be a sort of 'love hierarchy', at least in terms of how we put our relationships into practice, and in love the main thing I look for that makes me feel safe is consistency in someones' affections, poly relationships introduce a kind of inherent inconsistency that for me would just be inviting insecurity honestly.