I would personally love to see this at PTY. As it is, pax for all US-bound flights already have to undergo an additional security screening at the gate and are herded into a cramped and secluded boarding area. Even as GE/TSA-Pre, my family and I have misconnected in IAH a few times because of CBP delays.

Aside from a comment about waiting an hour in a sterile area prior to departure, I don't see a lot of complaints about pre-clearance on this FT board, aside from the same general rudeness we see at any point of entry.