It could frequently come out a big problem of collisions with existing templates with different code. I feel that synonimous templates, with different features, are a very subtle and harmful touble. This raises the long-standing problem of "redundancy and coherence" so deeply afflicting anything into wiki contents, but extension tags. It's impossible to leave to the willingness of bold, sometimes unexperienced users, the hard task to align templates. Exactly the same, for experienced users.
But perhaps, a "SharedTemplatesExtension" could be built, ensuring a common repository of template routines, matched with common names. I can't imagine how this can be done. :-(
Alex