TIL another awful thing about Linux procfs behavior; top-level /proc only reports processes (thread-groups) via getdents/readdir, but opening /proc/$tid where $tid is any thread id (not necessarily also a process id) succeeds.
Not sure, but yes they existed. Glibc's NPTL was a primarily a political achievement, not a technical one (it was actually pretty bad technically). Of course having someone even more toxic that all the kernel folks put together behind it probably didn't help the political aspect.