Add a third dimension in addition to Test Case and Test Plan, to identify a particular test case instance, for example the platform, or the device.
Which is to say that, inside a single Test Plan, you wouldn't have just one dimension, the Test Case, but also a second dimension, the platform.
So, let's say the use cases would be the following:
Add a Test Variation Dimension (any ideas for a better name?)
1. The User enters the Admin panel
2) Selects "Test Variation Dimensions"
3) Trac asks for a Dimension Name, defaulted to "Device" (or "Platform")
4) The User can add one or more values for the Dimension, much like it does for ticket statuses, milestones, etc. He can also remove any existing values.
Associate a test catalog to a Test Variation Dimension
1) From a test catalog, the User selects from a listbox the desired "Variation Dimension"
Display the status of test cases in plan, which has a Variation Dimension
1) From a test catalog, the User clicks on the desired Test Plan
2) Being the catalog associated with another dimension, the Test Plan page is in the form of a table, not a tree, with Test Cases in the rows and the associated Dimension values in the columns. In each cell, a red/yellow/green semaphore will display the current test case status. Initially, all test cases will be in the "To be tested" (yellow) status.
3) The User clicks on one of the semaphores and changes the status of a Test Case for the particular dimension value (e.g. platform).