Yes, we'll have fullscreen capability in the future. Scalers (like a 2x scaler or something like HQ2x) are not so certain for the classic port, since the code is so weird it's hard to implement without bugs.
We plan to make the code as portable as possible, and if SDL runs on the GP2X it can surely be ported. There may be problems with the screen size though. (It's kind of very hardcoded). It should be much easier on the enhanced port.