It seems that Disney is waiting for approval to expand the monorails between all parks before any changes to Spaceship Earth. The reason is budget. Since the monorail expansion costs so much, there simply isn't any money left for the SpaceShip Earth refurb. As a matter of fact, that is why the SSE wand is still there.
The monorail expansion will accommodate the influx of new visitors once the new, fifth gate is opened. This announcement is expected later this year. The new park, by the way, will be a villain themed park.
Of interest, the monorail expansion at Animal Kingdom will pass through the newly built Hogwart's Castle from Harry Potter... sort of like the way the monorail passes through the Contemporary - very cool. This will be part of the yet-to-be-announced build out of Beastley Kingdomme.
So... once these changes are made, SpaceShip Earth will indeed be made into a roller coaster... although the name is still to be determined. There is some debate within Imagineering about how to properly theme the re-design. One camp insists on going forward with a "Stitch's Rocket Rods" while another group is pushing for something based on the Pixar short, Boundin (details are scarce).
My source is an unnamed veteran of the WDW transportation system.
Hope this helps.