you forgot the rule of the untouchable 12....but Legend of Zelda is a different franchise with different rules.....and I believe Skyward Sword is going to be very big that it will make Girahim big to.
No, I object to this, the reason why I say so is because the original 12 arent necessarly protected, to be more specific Jigglypuff isn't, why? because he was orinally going to be scapped in brawl hence why he was added so late in development, why would Sakurai do that if he were part of the original 12, while I think Jiggs is likely to return I also don't see her as "guaranteed" by any means, Ganon wasn't in such a situation because he was never planned to be cut to begin with.
Also, I don't see a problem with Ghirahim and Ganondorf co-existing, you state it as if Ghirahim will incorporate Ganon's moveset or something which i doubt, the way I see it is like so..
Link (shoe in)
Zelda/Sheik (shoe-in)
Y.Link/Toon link (either one)
Ganondorf (main antagonist of the Zelda series, iconic as well, has been in Smash)
Ghirahim/Tingle
I'd say it would be a fifth slot if anything since Zelda is a big franchise much like Pokemon and Mario are, it's also demanded by fans as well.