Wonderful idea. I do have to wonder, is Sora picking up Eraqus' Keyblade symbolic, or will he actually use it, and further more, if Sora is picking up his Keyblade, does that mean the Aqua is already out of the Dark realm/ left the dark meridian?
Definitely not new. That is, indeed, the same Keyblade left behind by Master Eraqus and, in turn, Aqua in Kingdom Hearts: BBS. It will be fun finding out how he came by the blade. It will be even more surprising if the story turns out that Sora forgets how to use the Keyblade if the held portion of his heart returns to the being it came from: Ventus. Technically, that's the reason he can wield the Keyblade, the connection he made with Ventus.