Re: Already under our noses?
Even better, you could start with a stdlib module before you went to the builtin. I've always cringed at the thought of a "decorators" module as some have proposed (which seems to me about as meaningful as a module called "functions" or "objects"). But a module to collect type-checking techniques would be ideal. You could then provide the same tools for earlier versions of Python (pre-decorators, pre-unified-types, etc.). Various names present themselves. Perhaps it should be a submodule of pychecker? >:)
Maybe the decorators could be part of the module that implemented interfaces, since we sure should get interfaces into the standard library before we start thinking about type declarations anyway.