But even if this 6502 OS mirrors CP/M calls in many ways, what good is it.
One thing I've learned over the years in the vintage computing world is to never ask "what good is it".
However, outside of the personal aims of the original author, CP/M-65 has a bit to offer the community.
The 6502 is famous for having a slew of "spectacularly incompatible" machines. This system is novel is that it does two things. One, it tackles the problem of the wide diversity of memory maps on the various machines head on with its relocatable binaries. 6502s are quite popular in the homebrew community. Z80 moreso, because of CP/M, but the 6502 because of its simplicity. This offers that community a foundation (for those that actually take it to the level of having a disk at all) on which to potentially build, well, anything they like.
Finally, it gets to leverage the 50 years of documentation within the CP/M community. In theory, any book on the operation and coding for the CP/M OS, should have pretty good relevance if the project is indeed as compatible as the name suggests. Sure, all of the examples are in the wrong assembly language, but that's a minor nit compared to understanding how the filesystem is laid out, how the TPA works, how the CCP works. That knowledge is all "portable".
It would be fun to see an Atari port, moreso as a proof of concept (no doubt it'll perform as poorly as the C-64 port, as the disk drives are pretty awful). But it would be interesting.
It can also lead more to a base architecture for a modern board, running a 8 or 14MHz 6502, with some kind of solid state file system. The Z80 community base goal is "get CP/M to run", because once they get there, they get the rest "for free". 6502 doesn't have that. Come up with a board and you have...a board. And maybe a monitor. Now, for example, someone could take the Fig-Forth CP/M listing and the Fig-Forth 6502 listing, toss them in a blender, and get "Fig-Forth for CP/M-65". They could do that port in an evening. Boom, native development on a CP/M-65 machine -- WITH an assembler.
Perhaps this will get no traction, who knows. Sure, there's no software for the CP/M-65, but, honestly, "so what". CP/M-80 has software, but little of it is used. "Great I can run Wordstar. Why in the world would I do that beyond 'Yay. Wordstar'?". The core lament of the vintage computing community.
It could fizzle, or it could act as a catalyst. Time will tell.