WireGuard only allows a single endpoint address per peer. This means customers who receive both an IPv4 and IPv6 address cannot use both protocols in their WireGuard configuration — they have to pick one.
If you provided a hostname per server with both an A and AAAA record, WireGuard clients would automatically resolve to whichever protocol is available on their network. This would make dual-stack WireGuard setups work out of the box without requiring customers to register their own domain.