I believe that this idea would have both positive and negative aspects to it.
Positive:
-It will make Game Development much easier.
-Those who wish to create new regions would have others already done.
-The regions could be edited as well, making due for a very decent fan-game. This, of course, means that the maps should be able to be accessible from the developer's point of view if he wishes to edit and perhaps add to it. This would require some specific mapping procedures from both you, the creator(s) of this Regional Starter Kit, and those who wish to create the fan-game.
-This would not upper the standards of a good game, as more and more people will get this SK, therefore making it the norm, and adding to the regions already created would be considered not the norm, and it can affect the game positively and negatively (As before).
-This will make it easier for developers to insert a better story, without worrying about mapping and whatnot. At least, not as much, though some people will take it to themselves to edit the maps as much as they can, in which they will be congratulated for their efforts, good or bad.
Negative:
-There will be a lot of users who will create a game only based on those maps. Just add a story and some Pokemon here and there and voila, there's a (then crappy) fan-game. People will frown upon such achievements, and will put to excess the principal of editing the starter kit to the extent that it is considered a more original fan-game. This is, of course, a Starter Kit, which means that it needs to be edited in order to create a game. A mapping SK, like this, requires editing to be original. Therefore, this SK, being a Mapping Starter it, would need to be edited in order to be good.
EDIT: I was away at a doctor's appointment, so let me continue.
Here is some advice.
-After you're finished, go to the Game Creation Resources thread, and post it there. Ask the Mod controlling the main topic if he or she can also put it on the first post, for a decent reference. Of course, create a post on the thread before you ask him/her. You should also wait until the SK is a little more popular.
-Post some screen shots, and try to add as much information as possible. Decorate your post with pictures, colored text and all that. Maybe even pictured headings. This will increase revenue, and more people will be accepting to download it, and thereby see it's awesomeness.
-Create "siggy" images for support and further revenue of users coming to your post.
Something that is a MUST for you to do:
A while back, I opted to expand Blizzy's Starter Kit, which in turn affected me. I did not credit some various benefactors that were primary to the resources that I submitted. Advice: Credits. Lots of them. Create a text file in your project with credits to your supporters, give links to every forum post you've made about the project and credit all who have posted, give credit TO THE GIVERS OF THE RESOURCES, credit Nintendo, credit Poccil if you're using his scripts to create the Starter Kit: Give cred to every single person who has helped you with the project.
I congratulate you on wanting to create a Regional Starter Kit. Keep a lot of things in mind, but this is a great idea.
~Exteradude