IMO it'd be very handy for the notebook ui to somehow mark a cell that has been altered but not yet executed. I find myself making alterations in various places in the notebook and then either forgetting to execute one of them or forgetting where the alterations were and thus winding up with errors later on in the notebook when I execute cells.
Perhaps a heavier border around altered & unexecuted cells would work.
Not particularly important, but a nice feature to have.
According to the last meeting, we have to change the milestone of this issue (the PR was already changed) to 3.0