He'll have the money to do it. He'll get significant support from outside the GOP. He'll want to participate in the Presidential debates. He isn't returning to Congress after his current term. Inflation, he believes, will be running "high." With the right VP choice, he could garner strong support from the OWS crowd. He'll be the only anti-war, pro-civil liberties candidate.
It could be very interesting. He doesn't need to win for it to be interesting either, and if he could beat one of the two, the GOP candidate, or Obama, he could really push the debates further along than he already has, i.e., he could shift the GOP further toward a fiscally conservative, socially liberal position.