AE isn't coming back for a few reasons:
It doesn't fit in with the Fantasyland East theme of the current Tomorrowland
Neither Does CoP, Space, TTA, Speedway etc.
It was an original attraction without a movie/TV show tie in
So? EE is and so was MS.
It would show that Disney would be admitting a mistake
Light Magic? Rocket Rods? Adding more Fantasmic! shows? DCA makeover?
Even as horrible as SGE is, it does provide an outlet for selling merchandise
The same merch that can be bought everywhere else and is just flying off the shelves right now in this economy.
A lot of people feel that an adult based attraction has no place in the Magic Kingdom
Good for them.
It would have been a ton of money wasted in turing the attraction to SGE and then back to its original form when it could have just stayed as is to begin with.
The Stitch AAs would be used at the new Tiki room apparently. That's where most of SGE budget went to anyway.
When SGE does finally get replaced, it will no doubt be replaced with a pre-existing character based attraction.
As much as I typically agree with this kind of cynicism, it would actually be cheaper and faster just to bring back AE than make a new attraction from scratch.