The question is, what benefit do they get from funding ongoing development of Solaris.
On Linux they can get features they want simply by funding them, but they don't have to fund everything, and they get the vast majority of maintenance and so forth for free. Given that, what's the benefit for switching everything they can over to Solaris?
Even if they now own Solaris, competing against Linux as a commodity OS is a death sentence. Oracle's value proposition comes from the products they sell on top of the OS, not the OS itself. Given that, I don't think it makes sense for them to be in the OS business.
I'll bet the same thing for Solaris that I do for SPARC: they put it into maintenance mode to fulfill their support obligations, and let it slowly fade away.