1. It should not use public internet address space 2001::/32. It's better to use private address space, for example: fc00::/7.
2. It should contain some "magic numbers". For example SLAAC address has FF:FE in it: https://en.wikipedia.org/wiki/IPv6_address#Stateless_address_autoconfiguration

I suggest using DNS SRV record to store port info. It's a internet standard and is more likely to be accepted by client apps. But it requires more code on the client side, and some DNS providers may not support SRV record.
https://en.wikipedia.org/wiki/SRV_record
https://www.cloudflare.com/learning/dns/dns-records/dns-srv-record/