In the last week I have developed a prototype USB Arduino format board using a PIC24 or PIC32 as its CPU. The Arduino format consists of the standardized 8 and 6 pin headers for I/O and power. This was accomplished starting with an empty Arduino shield prototype board and building up as a PIC single board computer instead of a shield. Now standard shields can be attached to this board.
The two CPUs I am targeting to support with this board are PIC24FJ64GB002 and the recently released PIC32MX220F032B.
The power circuit, ICSP (on left), and USB have been tested. The PIC24 running a CDC (Serial over USB) project is recognized by the host PC. Next step is to test the FTDI serial connector (on right), and all the analog/digital pins. Following that is to add a crystal and capacitors to get USB support for the PIC32 (I wonder if I can do that on a shield?). All pins are exposed via the Arduino shield interface, so it is super expandable. The red LED is for 5V power, and the green LED is for 3V3 power. The button is the reset switch. No user I/O are provided, must be accomplished by add ons.
The missing piece is the Arduino development environment support for PIC24 and this low end PIC32 chip. That's a pretty big missing piece. For now I can develop using Microchip's MPLAB 8 and MPLAB X. I am hoping to use the chipKIT Arduino Development Environment for this board soon as it would be nice to program with Arduino sketches and C++.