I think the F-117 would just be boring. Nothing new, just another close air support/attack aircraft, only with less weapons and not even a gun.
EDIT: I do agree that the F-117 is an awesome and interresting aircraft, but that is not enough to make a good game that will be fun to play. Variety is the key to that, we've done the CAS mission now with both BS and A-10C, an aircraft with another type of mission too (air-to-air, dogfighting or something) will be needed to keep the DCS series interresting and fun.