I had heard about it leaking earlier on GameFUQs but the link died before I got to it.
And speaking of GameFUQs, a few spoilers have been dropped about the game already (since the game broke street date in Japan and is out now).
Characterwise, what we've seen thus far is what we're getting and nobody's sure that we're even getting Cia, [s]Orko[/s] Wizro, that other guy.
Ruto, Agatha, Zant, and Ghriaham are unlocked through Adventure Modo and have almost no presence in Story Modo, Ganondorf unlocks at the end of Story Modo, probably after you beat Ganon.
Lana/Cia pulled a Dragon Ball's Kami/Demon King Piccolo and separated themselves from each other. Much like Dragon Ball, Cia dies at the end and the plot gets Hijacked by Ganon.
The Master Sword is Link's fifth weapon and is unupgradable; nobody seems to know what his fourth weapon is yet; Link, Zelda, Impa and Lana are the only characters who get more than one weapon type/move set.
It looks like you can hold up to 30 heart containers.
Edit: Character Count Confirmed. Link, Zelda, Impa, Shiek, Lana, Midna, Fi, Daruina, Ganondorf, Ruto, Agatha, Zant, and Ghiraham are all we're getting this time. Better luck next time in Hyrule Warriors Xtreme.