The Disneyland Resort has filed a permit with the city of Anaheim that references construction work to both Space Mountain and a 5,000 square foot indoor space nearby, which is likely the former Starcade.
The current Space Mountain queue runs up a ramp, then across an outdoor rooftop deck and next to the former Starcade building, before heading back inside the attraction building. Rumors suggest that Disneyland will be taking the unused upper level of the Starcade and creating additional queue area for Space Mountain.
There is no time table yet for the construction, but with HyperSpace Mountain returning on May 4th, the extra air conditioned space could be welcome.
Currently, the lower floor of the Starcade building is a flex-space that can be used for private events or meetings.
Source: City of Anaheim