Currently in RetroArch Wii, GC, and others you can alter the resolution but there’s no way of selecting the following:
256x240 256x224 160x144 256x192 320x224 320x240
Also! There lacks a option to set a resolution, but then chose to go for pixel mode thus getting pixel perfection such as 320x240 for a NES game which is 256x240 (or 224) and having black bars for perfect pixels.
I myself and a lot thoughts would really appreciate these two features if they were to get in. I’d be willing to donate a little money to the cause if needed as well. Thank you for reading. =D