Sheik is the only character who's from a big franchise who isn't an active character in her series anymore. Can't be said about any other character, so I still see her as the weakest link. Also, Impa's role has become more important than her in the meanwhile, so it's the only logical "replacement" I could think of in the roster.
Matter of fact is that Lucas was supposed to replace Ness in Melee if Mother 64 would've been released. So funny how you mentoined him there. Ike and Chrom was a situation that could've easily happened, but unlike Sheik's case, Ike is a far more important character to his lore than Chrom- yet everyone was extremely sure this would happen...
Anyway, I could still see Sheik getting kicked out for Impa if the latter appears with a role in Zelda Wii U and Sheik does not. Only saving grace could be Hyrule Warriors, in which Impa also appears.
Yeah they could appear alongside each other but the Zelda roster really, really needs some freshness in the roster it's been stale since Melee really, so it's still a sacrifice I'm willing to make. Yeah, it's an unpopular opinion but IDGAF. Zelda is a big enough franchise to warrant more playable characters, and if one has to be sacrifised I choose Sheik due to her being the least important in the series, even if Ganondorf has the worse moveset.
Speaking, I still think it's ridiculous that Sheik has had more love given to her than Ganondorf or Toon Link, despite both of those two characters have more importance and far more to work with.
But yeah guess y'all like Grenades and Bouncing Fish too much eh?
Her being Top Tier again puts this whole ****uation back to the post-Melee, pre-Brawl era where Sheik is just being clinged to by the fanbase because of "popularity" ignoring anything else in the process.
I know Impa is the most likely Zelda DLC character, which means it's far more likely to see Impa appear alongside Sheik than her appearing at all, but yeah I still think this whole situation is just screwd up.