> 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.
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.