Extremely unlikely, but yes, of course it is possible. There are probably only Nibali, Rodriguez, Wiggins, Menchov, Van den Broeck and Scarponi left out of the original contenders who can realistically win it (and of them I think only Nibali, Wiggins, Menchov and VdB could be described as having a "realistic chance" of overall victory now). Mollema has done well on the steep stuff and on the even steeper stuff and can apparently do a decent time trial. Plus he seems to have a burst that has already got him sizeable time bonuses and Rabobank looks capable of providing a lot of assistance.
All of the above (except Mollema) have lost decent time on one stage or another and all are capable of having a bad day in the weeks ahead - there is absolutely no stellar contender in this Vuelta, with all prone to inconsistency. The chances of them all having one disasterous day and Mollema not having one seems highly unlikely. But you can't rule it out.
On the other hand there are other rank outsiders that, like Mollema, can't be totally ruled out too; Kessiakoff, Froome (if Wiggins bombs) and possibly Fuglsang, Nieve & Cobo. We seem to be adding almost as many challengers as we are losing. If Mollema can get a top 10, he'll be doing brilliantly.