So we all know by now that a DT within an assembly cannot control dimensional values that are within a part file.

The only way that I know to do so is to leave items that you want to control by a table undefined at the part level.  Then within the assmbly you would create sketches with dimensions that are linked to the DT within the assembly.  Correct me if I am wrong, but this is all fine and dandy unless you plan to use one of those parts in another assembly and want to assign it different values....correct?  This just does not seem like a stable way to design parts that you want to use in multiple places.