Kimi seems to be back in F1 on his own terms now and dosn't have much to prove. Where as before he seemed weighed down by the job of being a Scuderia driver, perhaps if he went back it would just be a case of rock up and drive.
He's proven this season that after his time out of F1, he's still got "it" and his performances clearly justify a seat at any of the top teams.
McLaren never suited his style or personality, and Red Bull seems like the best fit but, given the chance to lead a Ferrari team on his terms, would have to be a seriously tempting offer. Get a young gun in to replace Massa and with a blank sheet on the technical front given the new regulations, it could see an up turn in fortunes.
It still begs the question, could Alonso and Vettel work together? As I've said before, I could say that racing relationship going the same way as Prost / Senna but it would be an awesome thing to watch.
The best thing is, that with the new engine regs, which will significantly change the way the cars handle and are driven, it's all bets are off. So, what seems like the plum move this season could turn out to be a dumb move next year.