I went and added a bunch of tiles from EasyRPG as another Tilemap Town sheet, and defined a bunch of the tiles in-game for the build menu. It's really cool that there is a drop-in replacement for the RPG Maker 2000/2003 tilesets, and that this part of it is public domain. This means there's a whole lot more tiles to pick from that have autotiling available.

I also added a new experimental autotiling feature where a tile can signal that its borders should count as a particular autotiling type that other tiles can connect to. You can see this here in the screenshot, where ice connects to ice and doesn't connect to snow, but counts as snow, so snow will connect to it. I added this because RPG Maker 2000/2003 (and consequently the EasyRPG RTP) contains a lot of tiles that have autotiled grass surrounded by snow or sand or something.

Not sure if this is the best way to solve this but it seems helpful for the use cases that popped up from this tile set? We'll see.

It's also very difficult to make these tile sheet images because it's supposed to make sense to people but also autotiling requires tiles to be arranged in a particular way together, so there's just these 4x4 or 3x3 blocks that need to be together.