I started a line of thinking about tiles one day around Christmas, but never really pursued the thought because at the time it seemed unworkable, overly complex, or totally useless. I only mention it now in case one of you geniuses can rework one of the ideas into something fruitful.
I thought that instead of thinking about possibilities of features on a simple square tile, with 1 feature per side (the tile "universe", if you will), consider changing the universe.
You can change 4 things: (1) change the number of sides of the tiles, (2) change the number of features per side, and (3) change the scale of the tiles. Finally, (4) if you count making the game surface 3D instead of 2D. This isn't really workable, although you could introduce tile stacking but that would become far too complex.
If you change the number of sides to the tiles, the only thing I can think of that might work would be to cut the tiles in half diagonally, that is to make triangle-shaped tiles with 3 sides. The only thing this would accomplish though would be to make it much tougher to match pieces, and I see no real advantage to these half-tiles.
If you change the number of features per side, one method might be to double the size to 1x2 (length x width) making it longer so that you have 1 feature on each end an 2 features along each of the longer sides. This change wouldn't really add much possibility, but it would be easier than triangular tiles to match up. Useless, since I can't see how the combinations of features in the joined area would make any difference at all, since it's the joined sides that really make placement interesting.
If you change the scale of the tiles, you could either double the tile size length & width dimensions, which would make a situation similar to the above. Alternatively halving tile size wouldn't work because then it would bisect rivers and roads, but thirds might work, since the middle would match up with roads, but what good would the outside 2 thirds be? Useless.
So there you go, a gaggle of useless ideas. It's late, I'm bored but not sleepy, forgive my rants