Unix may never become big on the desktop, but that battle is still being fought and it probably won't be over for a few years. However we shouldn't forget where the large strength of Unix lies: the network. Unix -runs- the Internet. I don't think any other Operating System can say that. The Internet started on Unix, the Internet was built on Unix and unless something better comes along (and that implies that we don't have "better" yet) the Internet will die running Unix.
Of course Unix, like any other modern OS, must change over time to accommodate new technologies and methodologies, but I see Unix being more able to adapt in todays fast changing Information Technology world than other operating systems based on monolithic kernels.
What do you think? Am I missing something? Is there a Unix killer in the works that I might have missed?