This feature will cover a common scenario where manual Test cases evolve to automated Tests. In this case, the user can either change/select the Test type to see different definitions (refer to the configuration option: Delete test definition when changing Test type) or create separate Test issues to cover all the natures for the Test.
With Test natures, we plan to make it more explicit that multiple Test definitions can coexist within the same Test case. Users will also be able to set the current definition so that Test Runs are always created using the "current" definition.