The UI on this is lovely. What is keeping my office from switching to this is sharing ability. Instead of a file base system, consider having it work like google spreadsheets where I can create a link, specify if it read only or editable, and share it around. A nit pick. Your directions are well written and awesome, but when I create new items, please slide them down so they don't cover my ideas.
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...