That's a big set of goals, and I have no experience with FPGA design, which is the key to the retro designs of Stefany Allaire and so many others.
WDC still licenses and supports the 65C816, both as a standalone "hard core" and as a core that can be licensed for ASIC or FPGA-based designs. So they have a 65C816 + I/O chips + hardware integer multiply/divide and other things you'd want from a microcontroller, in an Intel MAX10 10M16 (16k LEs).
But I don't want to use their memory mapping.