My concerns are mostly caused by range limitation due to running a match in the single "bay" of an indoor range. I've run quite a few multigun and pistol only matches, and I don't think there is a way around long guns adding time to the match without compromising safety. Handguns in holsters provide a very nice bright-line rule for gun handling. Handguns don't come out of the holster unless in a safe area or under the direct supervision of an RO. This eliminates risks of gun handling behind the firing line and outside of RO supervision. The only way to provide this level of control with long guns would be to require long guns to be cased unless in the safe area or under direct supervision of an RO. Casing/uncasing will add time by itself and there will be more delays when a shooter doesn't realize he is on-deck and has to go get his case.
Here are some other issues that I've been thinking about:
Fixing a stage prop or unpasted target after "make ready" is more time consuming if the shooter has nowhere to put the PCC except in his hands.
CoF design needs to take into account people moving with long guns. It is much easier to get DQed while moving in certain ways with a long gun than a pistol. IME, most multigun matches are not nearly as strict about the 180 as long as the muzzle is pointed at the ground.
I also think the steel safe distance might need to be assessed with the increased velocity from PCCs.