Amongst other problems, that limits TLDs to 6 characters, which is about 16 characters shy of the longest TLD right now in the DNS root zone: https://data.iana.

Amongst other problems, that limits TLDs to 6 characters, which is about 16 characters shy of the longest TLD right now in the DNS root zone: https://data.iana.org/TLD/tlds-alpha-by-domain.txt https://data.iana.org/TLD/tlds-alpha-by-domain.txt Add to that the fact it would fail on a legitimate top-level domain like .рф or .中国.