I think something that adds simple door, stair, and treasure icons onto the map quickly and easily would be simple and valuable. They could sit over an edge or a cell.
I usually draw little things like this on my wet erase map, and I think its easier to understand at first glance for players joining in.
This would likely require another layer on top of the map so I understand if it would cause issues with the application architecture.
+1 On the Icons/a similar feature. While not essential it, would be nice to mark doors and the like (other points of interest that might be better served with a visual rather than a labeled map token) in the map beyond just colored backgrounds (I know I do at my physical table).
However, I might be a bit concerned about either feature creep (expanding to have too many icon options because people find the current set too limiting), or creating a bit of a painted duck scenario because GM’s feel obligated to add the extra details. So maybe something that has a similar effect, but would work around both of those problems would be better.