Just a hypothesis, because i couldn't "slant rhyme" effectively for an entire song; it's just not something I have the ability to do - With New York City still being the ultimate goal of almost every American theater lyricist, and with the Tony voters and New York City critics as a body caring not a whit (or wit) about true vs. slant rhyming, isn't the battle over and the anti-slant folks seem to have lost?
Seems to me doing REALLY EFFECTIVE slant rhyming, as the Book of Mormon writers do, is an art that requires talent and instinct and a strong narrative and book, and effective music, to make work. I wouldn't be surprised if we start seeing a proliferation of slant-rhyming dictionaries to rival the real-rhyming dictionaries. I don't have to like it, none of us have to like it, but the NYC critics and Tony voters and audiences seem to "has spoken" - if the book works, and the music works, and the slant rhyming is effective and doesn't draw you out of what's onstage, at least for now true rhyming doesn't matter to them.