I'm sure I'll get knocked for this (again), but if you want to pick nits, it's the GPL that prevents the commingling, not the CDDL.
Why not just say that the licenses are incompatible?
That's the simple truth, and that's not a slight on either of them.
The real problem here is that there doesn't appear to be an OpenSolaris development community outside of Sun^WOracle. It's much like Mozilla in its early days, though with an even smaller chance of success. Mozilla's competitive landscape was devoid of credible open-source alternatives - that's not the case for OpenSolaris.
Fair enough. Linux also can't borrow code from OpenSolaris. I would love to have ZFS on Linux.
Anyway, it was Sun who raised the possibility of licensing OpenSolaris under GPLv3 (that would still prevent Sun from borrowing lots of Linux code and Linux from borrowing any Sun code, but it would, at least, be a start) not the Linux folks who considered re-licensing Linux under a CDDL-friendly license, hence the "unidirectional" slant of my post.
As for the community and Sun^WOracle's contributions, Oracle has made it clear that they would follow an open-core model for the OS.
That's really sad, IMHO, but predictable. Ellison is nicer than Gates and way cooler, but it doesn't make him a particularly nice guy who wants to share.
BTW, I think the copyright fragmentation you see in Linux is one of its strengths. When you contribute a patch to OpenSolaris, do you retain its copyright or you transfer it to whoever controls OpenSolaris?
That's fair - Sun at least had the option of relicensing (given that the required contributors to sign an IP agreement).
FWIW, it saddens me to watch Solaris stumbling towards its grave. Remaining available only on hardware sold by Oracle renders it worthless to me.
I can't make that shift now, which means that I need to build my own credible alternatives to using Solaris. And when I am in a position where I could afford Solaris on Oracle hardware, I won't be so inclined - because I'll have my homebrew alternatives, and a bitter taste in my mouth.
But not even that would be enough to keep it alive and evolving.