I doubt this feature is being worked on much, and I wouldn't be surprised if it was added when all expansions are released. I hope for the opposite though, because like Ever Adrift, I too have mucked around with the annoying builder that is currently 'present' and after making two maps have given up. There is simply no joy in the effort that is needed to get the custom maps running.
It's a promised feature, so I really hope they'll introduce it asap.