It'd be nice if compilers were smarter about using the stack (looking at you, cc65) -- you could have "big" stack frames and little stack frames, pass variables in registers, push values as 8-bit instead of upcast to 16-bit, convert locals to static, etc.

I'm going to take a look at yet another alternative 6502 language called C02 now: https://github.com/RevCurtisP/C02