I'm curious, and I haven't found the answer yet - what's the scaling plan if Bitcoin Cash runs out of block room? Just keep increasing the size? Is there an upper limit before the chain increases in size too quickly to be sustainable?

It's the usual combination.

Block size as much as makes sense, optimizations where possible, if lightning works (it won't) - use it.

Gavin Andresen has published about his latest work 'Graphene' which shrinks block sizes dramatically.

They'll take/use any good ideas so long as it doesn't cripple basic onchain functionality.