So it may be useful to discuss what Illumos is, and is not.
Illumos is a fork of Open Solaris, but it's a fork of a special type.
A normal fork takes today's code and goes off in a new direction with it. Gradually the forked program and the root diverge.
Illumos isn't going to be like that. It will expand on and support what Oracle offers under the CDDL as "OpenSolaris," but if Oracle did a complete rewrite over the next few years, rendering what Illumos does in the meantime irrelevant, then Illumos will adapt to the new version.
It's more of a redneck fork, a fork whose family tree doesn't branch.
Nexenta is doing all this to push NexentaStor, which depends on some OpenSolaris capabilities. It's working with two other OpenSolaris distros, BeleniX and Schilli. It's a semi-independent operation, a software archipelago.
Illumos is sort of a cut-out for disgruntled Solaris customers who don't want to do business directly with Oracle but still depend on capabilities of the old OpenSolaris for their business models. As Nextenta does.
Not that there's anything wrong with that. But it doesn't make OpenSolaris truly open. Contributions to Illumos are subject to being cut off at the knees by the next Oracle release. Illumos will play no part in the Oracle development roadmap.
If you like that and need that, Illumos offers a welcome home for you. But if you like and need true open source software, to which you can contribute and have an equal relationship with, look elsewhere.