Hmmm, good question. I think having the fan be the actual propulsion unit would be quite kewl indeed but you'd need to change the AC motor out with a brushless DC motor. That won't kill the spirit of the thing too much but it's kinda necessary if your gonna use the fan blades as the primary power plant. Else I'd say do up a triple engine system, 2 brushless and the fan in the center at full speed 24/7.
You could even turn it into a multirotor if you want by installing a brushless motor on each fan blade. You would have to make a custom motor mount to negate the tilt in each fan blade, and you would have to lock the fan blades into position, but it would work.