Really dumb question from someone who barely knows this stuff, but does quantum computing in theory reduce that size again if it takes off in the future?
No. Quantum computers do not and can not solve the same problems as classical computers, so even if quantum computers were smaller (right now they're not), they are not substitutes. This is notwithstanding the fact that current quantum computers barely work and require a huge support system even if the computation part might be small.
