Browsers already know that abc.com is a domain under the .com TLD and abc.co.uk is a domain under the .co.uk TLD. If you don't believe me check the address bar and see how the something in something.abc.com and something.abc.co.uk are either in gray or hidden.
Therefore it could enforce this so that something.abc.com and something.abc.co.uk aren't allowed, as well as banning parameter passing using ?.
There, not too difficult. Perhaps the issue should be reopened on github again.