The language doesn't really have any opinion on that though?

But I could imagine assumptions about it being a problem if you try to add a 6502 backend to an existing compiler for other platforms.

Sometimes a source language can be an awkward fit for a target architecture. For one thing the 6502 is 8-bit and the C standard guarantees that the int type must be at least 16-bits. More generally, quirks of a hardware architecture can make it difficult for compilers to generate efficient code.