Nope, you don't need to, because of a simple fact that there is a very minuscule amount of IPv6-reliant systems in the wild. Most of them also operate in IPv4 (because IPv4 is more prevalent).
Not really, since IPv6 adoption is low, a service that doesn't also exist on IPv4 practically does not exist, so if you have a good migration path (unlike v6) from v4, you're taking approximately all services with you.
Comcast's entire core network is pure IPv6. Every cable box, cable modem, everything is connected and managed using IPv6 addressing.
None of it is IPv4.
T-Mobile's core network is entirely IPv6, IPv4 lives on the edge only.
Facebook's entire internal network is IPv6, they have IPv4 edges that translate to IPv6 internally so that it is routed as if it were IPv6 and all services see IPv6 only.
Sorry, but your "adoption is low" is very VERY wrong and IPv6 has already solved a lot of problems, for example the "we are out RFC1918 space, and adding more NAT is not the solution".
That last part is literally why Comcast moved to an IPv6 core.
Mobile networks, for example, have huge deployments of IPv6. Whether or not they are used to access IPv6-only services doesn’t change the fact that IPv6 is an integral part of their network design and therefore an alternative to IPv6 would need a migration pathway from it.
Name me an existing system where:
a) requires IPv6; but
b) not because of its long address.
Good luck finding such a system.