Due to the hierarchy of dns you can ask to a root server who handles .com, then to that server who handles google.com, then to that Google server, who handles mail.google.com, and then you can connect to it. If you allow anything to be a TLD the root servers need to know about everything, which isn't really feasible
> If you allow anything to be a TLD the root servers need to know about everything, which isn't really feasible
I wonder about that: The number of TLDs in my scenario would be approximately equal to the number of user-registered[0] domains now.
The .com root servers already need to know a large fraction of all 'user-registered' domains, and will need to scale to a much larger set of data as the number of domains grows.
Therefore, I expect that scaling to all 'user-registered' domains wouldn't exceed the root servers' capacity.
[0] I can't think of the technical term at the moment, but domains such as ycombinator.com, bbc.co.uk, ox.ac.uk, etc. Second-level isn't quite correct (see the .uk examples), and I know parsing the user-registered part is a bit of a challenge; see https://publicsuffix.org.
