Stuff like 6502s and Z80s are a bit like little single-cylinder engines - the world will move onto all sorts of interesting new places, but something somewhere will always be powered by a wee Briggs & Stratton that starts first pull of the string, and we'll be glad of it.
We'll always need tiny cores, but it's worth noting that RISC-V can squeeze down to pretty small sizes and is so much nicer to use. Notably you can go smaller than a 68k or 8086.
I suspect 32-bit RISC-V cores will become the minimum unit of processor for new designs. Not a meaningful cost increase over say a 6502 (or ARM) to build, but the convenience of having mainstream compiler support and that kind of thing does make a difference in the cost of building a product.
