That would be pretty great if done right. I would love the ability to put a full size slide on a compact frame. The SC has always seemed pointless to me but if I could put the compact slide on that short grip it would find a place.
Not sure of the engineering challenges to do this, but with a chassis they could have a super thin grip frame that takes 92 mags, and a thicker frame for those that want to run .40 or .45 with px4 mags, or who just want more grip surface for performance. With how the trigger group is already encapsulated and lifts out of the frame on the PX4, it seems to me turning that into a chassis wouldnt take a ton of R&D, but then I'm no engineer.
A chassis also solves the grip slickness complaints, as I dont need to start sweating at the thought of taking a soldering iron to my grip if I can replace it for $50 .