As the GB/GBC has 160 x 144 pixels but GBA has 240 x 160 I think there should be the possibility to set the full screen resolution separately for both platforms. Corresponding to that it would be nice to set the maximum magnification for each full screen resolution separately.
Think about that: If I set e.g. 320 x 240 as native resolution (I can set this resolution as I'm using an ArcadeVGA graphics card in a real arcade cabinet with a CRT monitor), the GB and GBC screen is very tiny with thick black bars around it, the GBA is a little bit larger on that resolution. As I definately want to use native resolution with no blurring or any filters there is at the moment no way to have the same picture size of both platforms on the screen.