Such a port would be so great
Solarus is already working on OpenPandora, and I think it should not be hard to port it to GCW Zero. We use libraries similar to the ones of Zelda ROTH/OLB/3T, but also OpenAL.
For libmodplug, make sure you use at least version 0.8.8.4. It might be hard to find so I have a fork here: https://github.com/christopho/libmodplug
In the next release (Solarus 1.1, ZSDX 1.7, ZSXD 1.7), I improved performance and portability. You can use the git versions (branch master) of them before the official release.
- Performance: I only use .it musics instead of .spc musics that were so slow to decode. (That's because I finally figured out how to convert them without quality loss.)
- Portability: you can set up a quest size larger than 320x240 if you want to occupy the whole screen without stretching the image or adding black borders. Actually, you can already do that with Solarus 1.0 but it is fixed at compilation time.
Don't hesitate to report any problems, like performance issues or problems when playing with a larger visible area like 400x240. I would love to help.
PS: where are you from in France?