homepage

It's clutter and we should show some restraint before adding new types.
Enthought's Python Distribution isn't shy about adding tools when they have a demonstrated need. Likewise, Django adds any reusable tools they need. Neither have a dict proxy. I've never run into a use case for it and haven't seen any feature requests for it. PyPi doesn't have package for it (at least not one with any uptake). The languages doesn't *need* this, nor do the other implementations which are trying to keep up with CPython.
Guido may let you put in it, but that doesn't mean you should. Again, I ask you to show some restraint. The language has already exploded beyond what fits into most developer's heads (even core devs don't even know about many the newer features).