They probably will have global maps for expansion only maps as to avoid the problem with previous maps. They will have to be converted and republished as an expansion map (even with no changes) to get the format. Publishers could make duplicate versions with slightly different names sure... but it would go against their own interests to do so.
I think you guys are mistaking global play for being a single server... It most likely isn't. It's most likely going to be like diablo 3 - You can pick what server you want to connect to in the options menu. I am fairly certain that servers won't be merged.
I know, I dont mean merged maps, I mean can I switch servers to publish maps? I know I have to publish it in each server, but if we can switch servers I dont mind Localizing it for that server and publishing it there too. It would be a great benefit. Also will US players be able to sign into the EU Forums.?