Question: Since the 32U4 has it's own USB host on chip, and assuming you're using a crystal oscillator on your own board, proper schematic & wiring, and the latest Arduino IDE build (which supports the pro micro/leonardo/32U4) then shouldn't you be able to program the bootloader over USB from within the IDE itself? Would this not eliminate the need for ICSP header pins and external programmer?
I'm asking because I plan on making my own project based upon the pro micro's ATmega32U4. I may or may not buy chips pre-loaded and this is my first project using the 32U4. In the past I've had to burn the bootloader on 328's over ICSP via an external programmer.
Just want to make sure I don't need to add ICSP pins to my PCB design before having boards made.