I hear that... Let me know how it works... Though I'd have to get my hands on the PLATO cart.....
If I understand it correctly (Thom will tell me if I’m wrong!), the PLATO cart has handlers baked in for the 850 R: handler, the 1030 modem and (I forget the name) the popular 3rd party modem that plugged into the joystick ports (Microbits?). It doesn’t/can’t communicate with a modem or device that loads its own R: handler otherwise, so the P:R:C can’t be used with stock PLATO stuff.
He’s reversed-engineered the code and has built some .car images that can be used with a flash cart that should work with the P:R:C but I haven’t had time to test it myself.
(Hope I got all that summarized correctly!)