I think "ALL" 16F and 18F might be taking it slightly too far as the PIC still needs to be able to "self write" AND it needs to have an UART. But what Dave is aiming at is the UMC bootloader in Microcode studio. It provides the "framework" for you to create a bootloader .hex file for any device, there's no longer any need to rely on pre-built files.

It's something I've yet to play around with but I see there are documentation available, always a good place to start.

/Henrik.