We know, and this is a generaliztion, that Jon's lineage isn't what it's said to be. I'm not saying Jon's a Targ coupled with a Stark, but he isn't a simple ******* of Ned's.
From the way Tywin, who put smart people behind him, reacted to Tyrion, I can't believe they were actually family. Tywin put being practical above anything else, and he knew Tyrion was more than able.
There only appears to be a few possible theories for Jon.
L + R = J
A + E = J
Or, as I mentioned in another thread, Jon and Ned (the Dornish kid Arya met who was his milk brother) were swapped at birth.
The only theory that would have him as one of the 3 dragon heads would be L + R = J. Otherwise, he may be just a central character that we have all grown to expect big things from.
However, him being bound by his current duty makes you wonder if
1) he will break his oath and joins the battle
2) the wall and watch is destroyed and he goes down with it
3) some of the remaining battles will be at the wall, to keep Jons character active
4) he is forced to go ranging (such as Mormont) and is swept into Battle
We still can't forget Winter is Coming, and those without proper provisions will starve as this may be a long cold winter.
Did I miss anything, if not, which side of the many fences are you on?