When selecting multiple cases at once in the Test Repository, it would be extremely helpful to have an option appear that says "Add to Test Plan." Especially in larger Test Repositories, it reduces the need for the user to keep track of where each individual case lives after creation given that they could be added at the time of creation.

The actual functionality could be implemented in a similar way to how you allow searching by External Issues (select "Add Test Plan," then select a preexisting plan from a dropdown, or allow for the creation of a new plan from this menu).