A great deal of mindshare has been eaten up by Linux. And Linux has largely "grown up" and has incorporated many ideas (and in some cases code) from the commercial Unixes. But I do wonder how many people are out there who have broad perspective and ability to push things forward at the OS level.
Also, back in the 90s I feel like systems programming was cooler and had more cachet. Even if people weren't actively writing code for their OS of choice, the icons of programming were the folks working on the guts. Nowadays, I think the cool stuff is all happening pretty far up the stack, and that there are relatively few people working on the substrate.
That's just my impression though. I'd be delighted for someone to look at kernel and system contributions to Linux, IllumOS, and the BSDs and convince me that there is sustainable mindshare to go around, and that all these OSes have a bright future.