Well that does work, but then people you dont want in can pirate your ideas while your working on it.
I could be wrong but it also doesnt allow people to work on the senario simultaneously. I know this would probably be difficult, but it would be nice and would incorage better senarios, less duplicates, and a better comunity.
Another nice option would be to be able to have land outside the map preset. If you start off with an african preset its imposible to enable land outside of the preset. I think it should be set up so that when you select africa it simply means everything else is preset to disabled.