I would second "cloud based" (cringe) saving and sharing. Whilst I'm personally not bothered about collaboration, I would love to be able to work on maps across multiple computers (with no Dropbox for local storage).
It's a dream to use, congrats on putting something so impressive together.
Saving maps online, sharing and collaboration is definitely something I'd like to add in the future.
But if I want to keep the offline editing capability (and I really do) these features are not trivial to implement. Synchronization and conflict resolution hell awaits...
It's a dream to use, congrats on putting something so impressive together.