You can make one biome having two borders generating at the same time, but it requires playing a lot with the NotBorderNear setting. All of the times I got two borders generating at the same time, it happened accidentally ... that shows the setting could be a bit easier
Also, in vanilla, isle biomes generate way more often to the edge of the main biome than in TC. Is that intended? (@Timethor ?)
Another nice feature would be an implementation of the "rare vanilla biomes" way of generating. On the biome map, some random "rare areas" are placed, in which Flower Forest instead of Forest generates, Desert M instead of Desert, Savanna M instead of Savanna. That doesn't work like that in terrain control.