Just turn it into parking lot!

I think future White House administrations could repurpose the ballroom as a parking garage, assuming the federal government could find the money to patch roof leaks to keep plaster from falling on the cars kind of like how RKO Movie Palaces were sometimes repurposed for indoor parking garages. After all, there is always a demand for more parking – go to any local government planning meeting and you’ll understand 99% of what government does is enforce parking minimums at drinking establishments and other businesses.