Nothing's realistically dropping support for v4 any time soon, so v6 support is optional. On the other hand, we're far, far away from all users supporting v6, so v4 support is not optional.
Running a single IP stack is infinitely simpler and easier than running two concurrently, and until that "single IP stack" can be v6, I see very little reason to support it.
Running a single IP stack is infinitely simpler and easier than running two concurrently, and until that "single IP stack" can be v6, I see very little reason to support it.