@Gargron The only way I'd like to see this happen, especially if you're going to let people opt-out of replies, is tie quotes to replies.

If a reply is boosted it should quote the post it's replying to for context when you see the boosted reply by itself in your feed (without having to click through to see the OP). That would allow people to quote post only by boosting a reply, which would also preserve your original argument against quoting in favor of replying.