The last holder of the PCC patent that I have seen is the Transit Research Corp. which was the 1949 successor to the Electric Railway Presidents' Conference Committee, the original patent holder and the organization for which the car is named. I don't know whether TRC still exists. If it does, and still holds the patent, then permission would have to be obtained and a royalty paid before a new vehicle using PCC technology could be built.
( As an aside, the necessity of paying royalties in order to build PCC cars is one of the reasons J.G. Brill Co. opted not to build the car and settled on building the short lived Brilliner)