From my standpoint, I don't see reason to have any of the four mentioned Zelda characters.
There's really nothing that separates Ghirahim from Zant pre-Brawl. Yeah, Ghirahim has popularity, but in the long run, he's still just a minor one-off villain overshadowed by Ganondorf (or in this case, Ganondorf's ancestor).
Same goes for Yuga, with the added factor of being possibly too late for consideration.
Which also affects Hilda, outside of being literally a Zelda from a parallel world.
Impa was really nothing more than a passing fad. The idea only became somewhat widespread when the concept of her taking the place of the Sheik alter-ego for Zelda started popping into the heads of some people, one of which that took it to the extreme.
Seeing as Impa in general is a rather minor recurring character with only two incarnations serving as particularly battle-ready (at which the latest incarnation isn't), as well as Link being mainly TP styled as in Brawl, not that much of a reason to believe SS Impa will be playable, let alone in place of Sheik.
As for Rosalina, I don't think it's that late for her. Unlike the above examples (for Impa, I'm specifically referring to the SS incarnation), Rosalina has had a while to circulate as to not be "too new" (debuting before Brawl was released) and has had a few recurring appearances. She's also apparently a semi-major character to Nintendo, seeing as she's one of five "Nintendo Starlets" featured on a 3DS puzzle (the other four being Peach, Zelda (Skyward Sword), Zelda (Spirit Tracks), and Pauline). Curiously, Daisy, who's been around much longer and more of a common name for Mario fans, was left out in favor of Rosalina.
Not that I'm saying she's the next in line to be in Smash, but she's not someone to take lightly, especially since she's implied to have an active role in 3D World.
So to make a long story short, if it were solely up to me, I'd take out Ghirahim and Impa, bring back Rosalina, and add Blue Toad.
EDIT: Or at least leave Impa due to the whole "recurring like Link/Zelda/Ganon" thing (even if it's far less).