So I did a few tests with 3x3, 4x4 and 5x5 but there was always an issue one way or another, such as no studs to hold the followers etc.
Ideal solution I could come up with, with my morning coffee was a 7x7 sized tile that only is 2 plates high.
First image shows how the board would look like. With 7x7 there is room for most if not all expansions. Center road piece could be easily done with 2 curved tiles to have two curved non-joined roads from, uhm, Abbey & Mayor expansion?
Second image shows all the components to build the first image. You'd simply pick these from assorted piles and place them according to image shown on card. One tile is now 9 one could say.

Third image is an example of how a card can look like, just need to add rounded corners and maybe stretch it a bit to fit a standard card size.
EDIT: I also realise that one could figure out what tiles are left by looking at the LEGO heaps. One could disassemble all the parts to really build each tile from scratch, though not sure it would help much.