Well, have to agree with you regarding Linux and POSIX. However, it's not the end yet. Although you can't officially call it Unix (mostly due to licensing issues) I stil think its fair to say that the BSD variants remain in a position which places them very close to that of a true Unix environment. Most definitely closer than your average Linux distribution (<cough>, systemd, <cough>).
And when looking at my personal favorite, which happens to be FreeBSD, I think it becomes more obvious why a project as this has little chances (personal opinion though). You see: several things which made Solaris great have slowly but steadily also found their way into FreeBSD. ZFS? These days I can even boot from a ZFS filesystem. DTrace? Full support available in the kernel. Zones? Well, it's not fully comparable to Solaris' zones but FreeBSD's jails do provide a very solid way to implement virtualization.
If you then look at the OS history then I think it's fair to say that FreeBSD has a larger one in comparison to OmniOS, and it's roots are already fully tied into open source. Even more important: there's no company involved with the FreeBSD project which also rules out possible double agendas (think about commercial interests).
I'm sad to see Solaris fade away like this though, it's always been my favorite Unix operating system both professionally and personally, but yeah... We got Oracle to thank for that one.