I think a placemat that is easy to wash would be the best. Becasue I have a drooling 90lb boxer I go through placemats like crazy! I typically like to get solid color placemats because it matchs my decor better. I think waterproof is a great idea but I do think fabric placemats that are machine washable would be nice too, this is what I like to use so I'd definetly be intersted if you start offering them
I dont know if this would be hard but I think a bone shaped placemat is so cute!