@TheNoof
I wish I could do a bit of relocation with the main PC chassis nice idea if you have the space and cables to do it!
As to why the PS/2 keyboard starts before a USB one, I have no real idea but have always assumed it is just because of the way the hardware is being handled by the BIOS, possible alphabetically rather than logically. Or, because BIOS is a throwback to the early days of computing, the code writers still use a base code from a time when only PS/2 keyboards were available and have "tacked" on to it USB Keyboard/mouse support. But, as I said, I'm really not sure and I doubt you will find a definitive answer.