I don't think the Smurfs hold any more relevance to popular culture today than ET does really. If they want to add Smurfs in a new building, then fine. But replacing ET with Smurfs is just replacing an old ride for no reason.
If they want to replace ET, I think they'd be better off with something like SpongeBob. Hell, I think the whole Kidzone should be torn down and replaced with a Bikini Bottom area for kids. A SpongeBob dark ride for the family wouldn't be a bad idea. I see SpongeBob advertised with Universal a lot but the only SB theming they really have is one gift shop lol.