Deep within the recesses of my foggy memory, I remember something
   about the u. structures in kernel memory being changed to a
   different format, [...]

In Net/2 and later, the struct user is now stored in a per-process
location, not a fixed location for all processes.

   I remember a short-lived libpthread at one point in time, but it
   hasn't been around for awhile.

It's still there!  Perhaps the author would care to comment on what
his plans are with regard to it.  B-)