>What would a society that supported waifu look like?
It is in a way somewhat supported now. Nobody calls it waifu though, they call it religion. I was raised Christian and theres a lot of similarities between a god and a waifu. Unlike the religious we (or rather, most) don't believe in their waifu's existence. Regardless of that it's similar, the sense of companionship, desire to please them, the sense of loving and being loved. Whether gods exist or not people who follow them often get that joy out of it, waifus fill a similar role. Of course you're treated as crazy in current society if you don't believe in god, but if you have a waifu people act like you're completely insane.
I think like >>16799 said it'd be better for everyone. A lot of people rush into relationships just because "It's what you're supposed to do.". Same for having kids. For all the acceptance western society likes to boast it has we're still very pressured into relationships/having children. It's gross, most normals don't seem to care about relationships past spreading their genes. The amount it's pounded into your head since childhood that you have to follow suit doesn't help. People have been catching on though, look at declining birthrates, declining marriage rates, etc.
>Would it be easier if everyone had a 2D love? Or would the pain be as bad even if it was shared?
It wouldn't make too much difference. It'd be nice not to feel pressured to get into a relationship/have kids or feel like you can't mention it to anyone. Other than that waifuism isn't painful to me. Its made me a lot happier.
>There would still be the problem of competition though
For some people, a lot of people seem to not mind it since as you have your waifu for longer your perception of who they are, how they act, can drift away from their source material. That being said I still get mildly jealous when I see other people mention her even though my view of her is quite a bit different from her purely canon version.
>Regardless it'd be interesting if not anything else, /mai/ is nice but waifuism can go a lot farther.
It might get a little bit more popular. At current people who take waifuism seriously probably number a couple hundred-a few thousand worldwide. With factors like declining population growth, declining marriage rates and even declining dating we might see it become a slightly bigger thing. I don't think it'll ever become more than a small group though.