One possible future for Solaris
In light of recent developments, here is one pessimistic view of a future for Oracle's Solaris. I wrote before that I didn't think that Oracle had suddenly decided to get into the operating system business; instead, they might see Solaris as infrastructure for their actual products. Well, take that to its logical end point and what you get is Solaris as Oracle's captive operating system.
As their captive OS, Solaris exists to run Oracle products and not for much else. It gets improvements only when they help Oracle's products (because otherwise they're not cost justifiable; operating systems don't make much money). In particular, it only gets new driver support for hardware that Oracle is interested in Solaris running on, which is probably only hardware that Oracle makes and a few other high end things.
(My native optimism says that Oracle won't entirely give up on Solaris on x86 hardware. But then, I thought that it might be six months before Oracle made Solaris non-free and it took them a lot less than that.)
This is a terribly pessimistic view because it basically predicts the death of Solaris through irrelevance, due to people not being able to run Solaris or OpenSolaris on common inexpensive hardware because it doesn't have the necessary driver support. (This is already somewhat of an issue for Linux, of all operating systems, and it's only going to get worse for a less popular one. Yes, even on server hardware; Ethernet and (E)SATA drivers don't grow on trees, among other things, and Solaris already has problems on Sun's own hardware.)
(As Pete Zaitcev notes, the much more important question for the open source world is what Oracle does about Sun's important open source projects. I care about Solaris's future for entirely selfish reasons, namely that we run it as part of our production environment and there is no equivalent replacement for our ZFS setup.)