UNIX, as a viable OS model, isn't the last word in operating system design. It has too much design decisions and other baggage rooted in technology dating back to the 1970s. As Rob Pike, one of the people who worked on UNIX, said "Not only is UNIX dead, it's starting to smell really bad."

On top of that, Linux essentially sucked all the air out of the UNIX development space by killing off all the commercial UNIXes. Carrying Linux forward rests largely on the shoulders of the kernel team and whatever contributions other businesses feel like making.

So where is the next major OS coming from? Google and Microsoft are the last two companies with the talent to build a future OS and enough resources and clout to push it enough to get traction. (In theory, it could also come from the community but people like Linus only come along once in a generation.)