Currently, the tile map is pretty hard coded for 16x16 tiles for performance reasons - a lot of the calculations are made significantly quicker by bit shifting / etc.
That said, 8x8 would also work for perf as it’s still a power of 2, and most of the values are already generalized pretty okay to support switching the size (though I’m not sure on how we’d have blocks to support that without things getting wonky - maybe just an optional parameter that lists out 8x8, 16x16, 32x32). Will take a look at this to see what we can do 
(partially there https://github.com/microsoft/pxt-common-packages/pull/855)
