Disclaimer : I don't work on Solaris nor Illumos at the moment. But I wish I were.
I've been working on Solaris for 4 years, implementing zones and then being "the Solaris guy" in a big software company. We had a bit of RHEL too, as well as VMware, and we had some AIX running, but Solaris (both in VMware and on physical x86 and SPARC) was 90% of systems. Back then I learned about Illumos and learned a lot from the community, from playing around with dtrace, and from browsing the code and watching talks.
It's been 1 year now that I worked exclusively with Linux in my new company. The other day at home I spinned up a SmartOS instance in my virtualbox at home, and in 5 minutes I was able to run different distributions in lx zones, and run dtrace inside them. I knew about those features for a long time but never tried them. What a breathe it was, I was baffled.
I follow the mailing list for smartos and omnios. You'd be surprised how little drama there is in those ; in fact, I don't recall having seen even one, in the past few years since I've subscribed. When OmniTI shut down OmniOS, in a few emails exchanged some people offered to create a community edition and that's it - the system lives. Some contributors (shootouts to rm ! but there are others obviously...), I've seen that can answer about a deep kernel issue in the matter of minutes, and have a fix under testing before the end of the day ; and I'm not talking about paid support here.
Anyway, my point is, if I could find a systems engineer job to do infrastructure work (or any work really) around illumos, I would snap call and go there. No more systemd, nwm, lvm, and poor implementation of docker to suffer. I don't care if the entire system goes down in 5 years (which it won't, that's the beauty of open source), at least I would have spent 5 years working on a reliable, consistent, stable system inside which, when you expect something to work a certain way, it actually works that way.
The post from Brendan, I can understand it. If your company has a strong IT team, regularly patches their systems, implement the new features of Linux, probably Linux is the safe bet. But where I am (leaving soon though), we still have some redhat 5.X (heck we even have some hpux...), and I would much rather have Solaris 10 even. Probably Linux is making lots of progress but the Illumos ecosystem is so advanced and "out of the box" that if I were building a company or advising one on their private infra, I would chose it above anything else, because I know I could scale it to 100s of physical hosts with very little operational overhead. Heck they are even implementing bhyve now, although they already have KVM and invested a lot of energy in that, just because bhyve is better.