The implementation will definitely need a up to date Public Suffix List. We control a bunch of public suffixes and it's a huge, huge difference if you browse to the address "www.com" or to "com" - or blogger.com and www.blogger.com, or dyndns.org vs. www.dyndns.org. In this case, there are different organizations/persons controlling these.
Should you not know which one you have connected to?
I think an exception list rather than a straight map is all that's needed. If you want to buck the convention, fine, don't expect the browsers to know what you're trying to do, so update this list, which takes 30 days to propagate, and you can have your fun.
Should you not know which one you have connected to?