Considering that there's the mobile phone version that we're discussing here, it seems one step has been made in that direction already. I think a Rockbox "app" version would be a great idea, but I do want to see the source to see how it can be done, and what will need to be tweaked further.
Llorean, I tried looking at the SDL website and Google, but no dice... I don't think (but I'm not ruling out!) that there's an SDL library for the PSP.