Yeah, the biggest issue with ALL true UNIXes...licensing. You see the be a REAL System V UNIX, you have share lineage with previous AT&T/Bell labs-based UNIX OSes. This was done by licensing and re-licensing source code for bits of the kernel OVER AND OVER AND OVER.
So, kind of like the Mortgage-backed securities scandal in the USA, no one wants to bother chasing down ALL THE IP holders of the current tech, and get them at the negotiating table to hammer out a deal to use this (obviously old but doesn't matter) IP to alter it in any way. If you buy the entire corporate entity, you don't have to do a thing (everything from the original licensee has been transferred to the new owner)...but if you want to separate the IP for SGI/Irix software out from the rest of the original entity...well. THat's a huge amount of work (legal and footwork).
I was told that (or led to believe) that this stuff (SGI MIPS specific property) isn't in a vault somewhere, that the Rackable Inc destroyed all the IP so as to not have to spend money to deal with relicensing. So I'm under the impression all the datasheets, designs, source, etc...is officially destroyed (outside of an ex-employee having an illegal copy from their old work sort-of-thing).
There was a brief public call on forums in 2013 for MS to buy Irix as a trusted OS status for government contracting from SGI (in final bankruptcy)...didn't go anywhere. Would have been a good idea to base the next Windows off a good UNIX kernel.
The machine designs have been destroyed, I'm pretty sure I read that somewhere. The Irix OS license, I assume it was purposely shredded to save a buck when Rackable Inc bought SGI, as Rackable didn't want MIPS stuff, only the name and I64 Linux junk.
I think bean-counting greed destroyed it all. The third-party IP licensing is the reason the OSes aren't opened up. The real UNIX kernel was based on a huge amount of work from many different sources, they patched a legal framework together to get it all to work, but no one entity owns all the rights to all pieces. Unless some kind of royalty deal could be worked out, that's the legal stumbling block to having the software.