The Galaxy Editor is not out yet however it is still possible to start working on maps. I will show you different projects that have already been started by the Mapster community.
Uberlisk by Hati
Remember the Uberlisk presented at the Blizzcon? They said it was really easy to do with the Galaxy Editor. It must be really powerful because many of us tried to achieve the same result with less success. Hati managed after many tries to attach one tentacle on the Ultralisk. This is the first step!
Artwork by Kanaru
In order to complete his project he needs custom models. However he is not only good at modeling he does quite remarkable artworks too.
MapGL by Technetium
Recent breakthroughs in Starcraft 2 terrain documentation gave an idea to Technetium: realize a terrain viewer. If you don't know him, he did the first BLP viewer for World of Warcraft and several work on MPQ files. The viewer is atm in early alpha but we can expect it to be functionnal soon!
ABout uberlisk complexity, we don't fully understand how certain gamedata components work yet. there is probably a fucking easier way we don't know of yet.