I guess this is the best place to jump in: I've been working for some time 
on a stupid idea, and it involves both the System V code (in the form of 
Solaris, although I've been attempting to theseus it out) and the BSDs.

One thing I've said a few times elsewhere is - if you want to do something 
daft, not only are you on your own, but people will actively not only 
dissuade but derail you from trying to do it.  I felt the best way to get 
what I wanted was to try to isolate the kernel and libc (and perhaps 
bootloader) from one of the BSDs and attempt to make them buildable 
through a system of plain makefiles, to integrate into the rest of my 
concept (this also includes, fwiw but unrelated, clang).  If you're 
familiar with Linux From Scratch - you can probably see what I'm doing, 
although it's not at all using the same code.  A lot of the time I keep 
running into "we don't want mere mortals working at this level" type 
responses.

Yeah, I know it's daft.  But I still want to do it. ;p

In fact, back in the Linux 2.4 days, I *had* a proof of concept.  But it 
ran on Linux and used a lot of "ersatz because copyright" which is no 
longer needed (e.g., because ksh and CDE weren't available).

I want my own flavor of Unix, basically... 🤪

The apparent death of System V is a double-edged sword for my idea.  It 
means it's all the more useless - but in becoming *useless*, it also 
ceases to be *pointless*, in my estimation.

-uso.