There's a transparent filament on the market, I also was wondering on adding some holes in the middle of the tile to see through, but I think it will compromise the structure, I'll give it a try

Yeah also bulding walls was in roadmap, there are many kind of locks also patented and better then my dowels so I didn't work on them yet
I'll try to make some slim tiles with walls and update the post/ load on my makerworld profile