I know you should only have a small number of mappers, but it's so hard to find mappers, and then it's hard to find mappers who will map for your game.
Eventually there will be some combination of stock tiles and custom tiles, in a sort of "thematic tilesets." For example, Orange Islands would use a Tropical Beach tileset. Kanto would use an Urban Subtropical. North Sinnoh would be Evergreen Winter. And so forth. We need spriters and tile artists to make that happen, and it's a fairly huge task.
For the time being, all we have are stock, Don Patch, and Saurav.
Yes, I would like each mapper to map out a large section of each region to minimize discrepencies.