You know, after having missed out on the last Vuelta because of the whole team situation I think he is quite keen not to miss this year's one. He has already said he is interested to do the Giro next year, and the way he enjoys cycling, he probably doesn't want to sit too many Giro's out in a row either. He loves the big events with tradition and history. That he wants to do the Tour next year seems logical too.
I'm trying to come up with an argument why he wouldn't give 4-in-a-row a shot, all the more as he seems less inclined to take "not winning one" as a personal failure as some others.
If anyone would be able to pull it off, or come darn close trying, he seems to be the guy. IT might depend a bit on what happens at the end of the year with transfers and stuff, but I'm sure the head is willing.