You know how the reboot Thomas is in 2d and most people don't like how he looks? Well there was an older 2d thomas shown in promotional material which I think is what a 2d Thomas should look like. It's accurate to the Thomas we all know and love, the face is simplistic, but in a good, recognizable way. It wouldn't need all of the shading, but still a bit to make it look nice.
I also think most of the designs in the books would be really good too!
I also think most of the designs in the books would be really good too!