Well, I have GPE up and running now. And the verdict is... oh, dear...

The good news is that GPE will *just* start in 32MB of RAM. The bad news is that trying to actually do anything results in the system chugging badly, as Linux frantically discards text pages and reloads them over USB, and ultimately crashes.

I tried giving it some swap, again over USB, and it didn't crash any more --- but it's awfully sluggish... you wouldn't want to use it in real life. The most expensive app was, as you might expect, Mozilla Minimo which idled at about 6MB. Embarrassingly, the Watch app, which draws an antialiased clock face on the screen, can only update the second hand about once every two seconds.

The good news is that I suspect this was extensively stress testing the kernel, especially the USB subsystem, and it's all fine! (Although the screen colours are screwed up due to 444/545 mismatch.)

I should give Opie a try to see if it's any better.

Would anyone be interested in the kernel.conf and filesystem patch I used to get it running?