A reliable source of mine that works at Disneyland Paris has informed me that Captain EO WILL be coming back to Discoveryland to replace HISTA.
Not sure when but apparently it has been confirmed (behind closed doors).
Also, higher management is already looking at the 20th anniversary of Space Mountain in 2015. Apparently they want to do "something big" and they are looking back at the original.
Again, these are only rumours however the Captain EO one did come straight form the mouth of someone who IS in the know.
Lets hope they come true.