Just a thought, maybe you need both the Wii U AND the 3DS in order to achieve all of the maps? I mean, wasn't that the way people were able to obtain Mewtwo? Perhaps there's another way using that method that people are able to achieve maps with the 3DS.
I know people who have 3ds and WiiU versions, and they don't have any more maps than I do. The maps that are exclusive to the WiiU are mostly for more people, since they're big maps. I hope that there will be an opportunity for 3ds users to have the maps, but it makes sense for them to make the larger 8-player maps for WiiU only.