Originally posted by reh321 Why would they require different lens lines??
Canikon users of APS-C cameras routinely use lenses designed for FF.
Pentax could easily release only lenses designed for FF in the future.
APS-C users would have a choice between purchasing from the currently-available line or from the FF line.
The problem is several fold. It is an entirely different mount. To use existing APS-C lenses on a micro four thirds camera would require either an adapter or to release the current lenses with a separate mount (which would get confusing). Part of the point of the micro four thirds mount is the decrease in lens sizes you get from a shorter registration distance -- this would not be the case with current APS-C lenses. Finally, the crop factor means that there are no lenses in the system that are really wide enough for that size sensor. You really want some thing in the 6 to 7 mm range for wide angle purposes.
As to full frame, if pentax releases it, certainly the current DA lenses will not go away, as APS-C isn't going to suddenly vanish. They will continue to be sold as APS-C lenses (most brands have a group of lenses that are APS-C only). However, I doubt that there would be any new APS-C lenses released in that situation, with new lens development going to full frame lenses.
Obviously, you can mount either DA or DFA lenses on any k mount camera without an adapter, the results that you get would then depend on the lens.