Originally posted by Winder Pentax could make a 50-135 f/2 for APS-C that would be the same size as the 35-100 f/2. Both of those lenses are a telecentric design which adds to the size and cost. It would be a $2,000 zoom and there would not be a size or weight saving over the 70-200 f/2.8. Is that something that Pentax users would buy? If Pentax plans to make APS-C their "professional" option then I think they need to.
They could but not with the K-mount, the register is too long and the mount opening is too small, if they shoten the register distance and make a larger mount opening they should be able to do it.
Best thing is because the register and the mount will be shorter then Sony, Nikon and the Canon aps-C+ mounts it means that you can fit their lenses on it with an adapter.
Canon lenses would be hard because of the many electronics but Nikon and Sony don't differ too much from Pentax.
So the lenses you can use grows a lot and it's easier for other brand users to make the switch.