Especially that the people who will restart from a Z80 will face technological edges when their skills and needs grow.
We faced the same in the 80's: going from 8 bit to 16, then 32, having memory addressing problems, being pushed to new and hardly compatible architectures, having programs to rewrite...
Then why not leaving behind us a technology, still simple, but that will save them most of these issues?
I feel an 8-bit data bus and 32-bit address bus would be a good way to make long-live programs, edge-free when extending memories, and still not so complex processors and main boards. The address bus does not need to be fully wired in the first processor versions, so it can scale over time with more complex processors when skills and needs grow.
Besides, it would be smart to leave in a vault a kind of FPGA technology with sources to flash the FPGA components. So no need to create a production line for many different integrated components: only one output, and the components are specialized by flashing them.
Indeed even microprocessors can be flashed on an FPGA.
Well, just ideas...
Low tech CPU to support 32 bit code:
https://en.wikipedia.org/wiki/Motorola_68008 (8 lines data bus, 20 lines of address bus, 32 bit programs, 70 000 transistors)
Microprocessor on an FPGA: