As in this century, friend, so just the non-canon Melee.Last century....I believe OoT came out last century...I believe SSBM is this century, too.
Sheik = OoT Zelda
Zelda =/= Sheik
It's not really a major part of her recurring character, so what's the point of forcing them to be connected again? I'll compare her to Mario again since they have a lot in common.
They're both the title characters of their respective series and have a major role as a recurring persona.
Now, imagine that instead of Zelda with her Sheik costume, we had Mario in a frog costume. It would offer a unique moveset along with his original and would give him some extra appeal. However, just like Sheik, that frog suit only appeared a few times in the huge franchise and had very little significance to Mario, especially at this point in time since it hasn't reappeared in years. Does some one like Mario, the face of Nintendo, really need a transformation when he's a completely unique, appealing, and deserving character all by himself?
Apply this to Zelda, you'll see it's the same thing.
Transforming into another character is simply a gimmick that's already been confirmed among other characters. Zelda's still a viable choice for a playable character all by herself.
At least Sheik is a different Zelda from the TP one, whereas Young Link and Link were still the same Link. It actually would make more sense than them if Sheik was separate.First of all, shiek as a seperate character would be wasting a space for a different character, possibly a good Legend of Zelda representative (Zant, WW Link, Midna). Also, shiek and zelda are the SAME PERSON. It wouldn't make sense to have two different characters. Yes Link and young link might be the same person, but they're in two different points of time.