Just in case you get the wrong idea: I'm very grateful that you put CP/Mish out there. My Z80 retroboard project benefited from it (I used the ZCPR1/ZSDOS .rel outputs directly in my board's emulator, plus the project served as a useful reference source) with no contribution back.

I don't think it would have helped anyone if I'd tried to make it support my board in your build process. There's one of my board in the world, with zero users now I'm working with its replacement design. I already had a BIOS written for zasm, and no removable storage (socketed ROM might count as removable I guess) so I wasn't trying to build a bootable disk image.

If, say, I had a vintage Model IV and wanted to make disks for it, it might be a different story, but for a retrobrew z80 machine it's a good reference but IMO not a good basis for the software part of the project.