I usually create tilesets from various games. I also snag some from the various pixel/sprite ripper sites since the best i do manually is screenshot then cut/paste to my tile sets.
Anyways, just finished sega master system Ultima 4 and was ready to import the lot to GC. BAM! Figures i forgot the sizes are 8, 16, and 32 pixels only. SMS ultima 4 is the odd 12x12 pixels. Sure i can substitute other tilesets but if i was to send an authentic ingame to say VG maps I'd have to use a different mapper.
Short.... Maybe add 4x4, 12x12, 24x24, and 64x64 options for importing (unless i missed something).
It doesn't hurt to ask!