Yeah and then you'd need to re-write major chunks of the OS to support the new hardware, plus you'd want some of the things that modern OS's have, so that there'll be very little of OS 3 you'd still be using....wait a minute..wait a minute...I think we've gone down this path already....
You'd just need drivers, not rewrite chunks of the OS. Ideally it would also be able to run in legacy mode where SATA appears like gayle ide or you could mount a hard drive image from a file on a USB stick and have it appear as a IDE/SCSI hard drive/cdrom etc.
The purpose of using SATA is more about getting cheap hardware than utilising all it's functionality, although if there was the option for that by replacing the scsi.device driver in kickstart then that would be great too. Even if it was just making it emulate IDE fix express.
I'm also more interested in a USB gamepad appearing like a 9 pin D joystick than being able to run a USB stack on the Amiga. Although if you could make the USB controller compatible with one of the existing Amiga solutions then that would be a bonus.
I'm not sure I'd bother with PS2, a USB to Amiga keyboard convertor would be better.
http://ezhid.sourceforge.net/amikbd.html http://www.amiga.org/forums/showthread.php?t=64931 The simplicity of PS2 draws you in, but it's actually just hassle if you're also going to support a USB keyboard. People will expect to be able to use a PS2 or Amiga keyboard, which are different and you'd need to configure it (without using a keyboard). Only supporting USB is much easier as you just detect a keyboard and use it.