Bad news, I got this response from Melabs.

Code:
We tried many years ago, but failed to make the USB commands work in a useful way. In any case there is no further development planned for PBP.

The 18F25K50 is less expensive than the 18F4550, but not as cheap as the 16F1454.
I wonder if they are going to stop selling and supporting PBP after they said "there is no further development planned for PBP". We use their U2 programmers and software a lot. I responded to their email asking if they will keep supporting PBP.