How long before someone realizes a redo of Spaceship Earth fits the MO of modern-day Disney?
If Tower of Terror isn't off limits, then I doubt any other E-ticket is. Not to mention, a redo of GMR pretty much would spell the end of lengthy, slow-moving AA-heavy dark rides outside of MK. SSE has no IP tie-in, and it's an icon a la the Chinese Theater meaning it draws extra attention. They never even finished the descent during the last upgrade.
One saving grace might be the operational headache that construction would cause -- maybe it would simply be too much trouble to do anything large scale to SSE.
I don't know when the Siemens contract ends, but wouldn't surprise me if it drastically changed within the next 10 years.