I think having a completely open domain would be a mistake--see PyPI (and particularly the (wx package)[https://pypi.python.org/pypi/wx/1.0.0] which to this day has still not been remove).  I think giving each domain control over their own namespaces *might* be okay, but I also kind of don't necessarily trust every organization to handle that in an organized way either.  In any case, in order for FINF files to be broadly accessible I think there would have to be some centralized registry of schema for FINF objects that FINF readers can regularly sync up with and cache.