I think polyamory is an immutable part of someone’s sexual orientation as much as the gender preference spectrum (homo/heterosexual) and the intensity/situationalness (ace/gray-ace/demi). I think some people just naturally see sex and intimate relationships as something they can do openly with multiple people and some people just don’t. I think it will become more acceptable for the people who see sex that way to find each other and express their love that way, the same as with all the other sexual relationships between consenting adults are becoming more acceptable. But the same way it would be silly to say we’ll all be homosexual eventually I don’t think we’ll all be poly someday either.