I’ve hung out with a bunch of Mormons and while they personally felt it was weird now, because they have grown up in a monogamous nation, the church itself would definitely gear up to switch back, if it was legal.
That would be a process, though. They are currently taught that it is morally fine, but following the laws of the land is important, and basically treat it like part of their history. On an individual level, the ones I know seemed fine with that, even those that had an active role in the church.
It’s also not that strange in more secular contexts, see this article about polyamory in general. So I think it makes sense for people to be okay with the concept of plural marriage, while not wanting to engage with it themselves (e.g. it wouldn’t work for me).
I suspect most of the time, non monogamy via religion is going to be shitty. It’s probably going to favor men and be controlling.
I know many people who do consensual non monogamy in real life. Personally I don’t like the DADT or strictly-hierarchical modes
People who aren’t familiar with it say some pretty wild things about it.
My take is if you can have multiple friends, and you’re okay with your friends having friends, you’re like 80% of the way there.
The last 20% is likely to crash into “it just is, stop asking me to introspect this is uncomfortable and I’m mad!”