Personally speaking, I'm wondering what Michael thinks is in it for him.
The Ferrari is currently not a winning car (Raikkonens 2nd place at Hungary nothwithstanding), at any point he decides to enter a GP he'll have had no experience of the new car, regs, tyres etc, the chances of doing anything spectacular are fairly low, in my opinion. Even if he does, it will be 'of course, it's Michael, we knew he's that good anyway'.
With all that in mind, in what way does Michael think he can improve on his already god-like status, because to me there are only three possible outcomes:-
Wins/2nd place/DNF whilst in the top 2 on merit - General opinion: Michael is still a top driver (and by implication Kimi and Felipe aren't) = no gain, no loss
Finishes elsewhere/DNF without being in top 2 - General opinion: Michael isn't as good as he was = loss
Michael suffers a big accident having survived his 'first F1 career' with just the one biggie - General opinion: Shouldn't have come back = loss