ouch that sounds like something really hard to do hehe making a homebrew os, maybe with jailbreak in the future we will be able to have completely unlocked linux imo thats our best bet id say, or what does the devs think about this?
We can already run unsigned code and remount system paths, so if someone developed replacements of the right files, then why not? I'd say a Linux bootloader from GameOS is all but guaranteed. As for CFW, anything is possible.
As far as osx there would be no 3d driver, flex i/o driver, ide blueray driver (fat ps3's). before anyone mentions ibm's cell demo running osx, well who ever said the cell is running osx? That demo could have easily been rendered from a pci cell acceleration board in a normal ppc apple computer.
No one wrote a 3d driver for linux until now so it probibly won't ever happen.