Thank you for your feedback.
We already have a story in our product backlog to allow editing properties like tags, priority, assignments, etc. for multiple items. (Currently - Area and Iteration properties can be assigned to multiple items at once using the Assignments pane that's located just below the Filters pane on the right hand side of most grids.)
I added a vote from you for this item. There are other positive votes for it so we might implement this functionality in some of our future releases.
the Telerik team