This is *not* a discussion about TLDs or UX.
This is just a discussion for what are permissible strings for names in the name-record store.
First suggestion, lowercase alphanumeric.
Second suggestion, lowercase alphanumeric and periods, but only if you owned the suffix without any periods (so you can emulate subdomains). Still manageable complexity.
Also maybe lowercase alphanumeric and any symbols, with above suffix rule.
Stuff that currently appears after the TLD in your browser bar is not part of the name resolution and is independent of this system so it would remain the same.