What made them special is how they combined their hardware with their own version version of UNIX.
Hence why even trying to write portable code across UNIXEs wasn't as easy as many believe.
Irix had IrisGL, Iris Inventor, XFS and a few other goodies, before they became the Open variants.
SGI was also a big sponsor of the C++ STL work.
Domain Specific Architecture talk by Hennessy & Patterson, 2018 talk for 2017 Turing Award: http://iscaconf.org/isca2018/docs/HennessyPattersonTuringLec...
However I can say yes, we are returning to those days.
Thanks to the thin razor margins you see OEMs now selling un-upgradable phones, laptops, tablets, 2-1, leaving the old desktop PC for a niche market that gets smaller every year, mostly targeted at gamers.
Also OEMs got envious of Apple as the surviving icon of those days, all of them want to be Apple of their market and sell experiences.