Pick a professional ($$) C compiler for PICs and go ahead ad rewrite the Arduino libraries for it. There are many C compilers for PIC, and some of them are reasonably priced or have freeware versions. I'm sure the PIC community would appreciate Arduino-like libraries if you choose to make them open source. But as kg4wsv says, the lack of a "standard" set of open source development tools probably makes distributing something like the Fully-contained Arduino (AVR) environment so tricky as to be not worth doing. (You MIGHT be able to do it for PIC24/PIC30/PIC32 using the "free" gcc distributed from microchip...)