This is good news, but it's such a shame that the GP controls don't really lend themselves to trully 3d shooters. The memory issue isn't related to screen size. It's related to the assets of the game (for example the textures, and to a much lesser extent, sound).
How does the game play on later levels where there are more varied monsters (thus more textures for their skins and more sound loaded)?
However, there were a few mods of Quake that didn't really need the up/down axis too much (QuakeRally, and there was a sport like Speedball). Admittedly, these were developed for PCs that were above Quake's Minimum Spec, but they might be playable on a GP.
The alternative is re-jigging the maps and having an auto-aim system in (Quake was pretty forgiving within a cone in front of you, if you can somehow elongate the vertical axis of that cone, it may make it playable).