The reason it’s limited is because it is much, much, much faster if the tile size is a power of 2.
We could theoretically add support for 4x4 or 2x2 but I’m not sure how bad that would make performance; smaller tiles are always going to require more resources because there are more tiles to be overlapped with and more things to draw to the screen. 8x8 works great though, so maybe 4x4 wouldn’t be too bad.