Coming out of nowhere doesn't really mean anything. After all... Weapon Mastery and Cunning Strike both "came out of nowhere" and were accepted by the gaming populace. So it's not like some new system WotC offered up in the playtests were automatically going to be stomped out by the playerbase.
Instead... more often than not it was merely changed items that got rejected by the playerbase. Things that weren't new, but rather merely things we already had that they were just getting moved around (by categories or whatever.) And that's where a large swathe of the playerbase asked "What's the point?" I mean what was the point of grouping Classes together? What purpose did it serve that was substantially better than what we already had (for example)? To which the answer was "There really wasn't any." There was nothing substantially gained in creating Class groups or Spellcasting Power Sources to warrant going through all the effort of doing it in most player's eyes. So WotC ultimately didn't. And the fact that WotC could then make the case that it might have been (or was) connected to people's beliefs or perceptions of backwards compatibility made it easier to explain and/or justify why they have been rejected.
I mean, I hate to break it to a lot of you, but sorry folks... a lot of stuff that appeared in the playtests that you liked... the rest of us felt just wasn't very good or was pretty much pointless. And we told WotC that. I know you wanted more stuff changed, but the rest of us basically said that change merely change's sake was a waste of all of our time. And WotC heard that and listened.