Much of the internet still does not support IPv6, so most providers will give you an IPv4 address. In fact only a few providers even support IPv6 at all.

Even with IPv6 it's not a huge problem. With a few samples we can know that a provider is operating in a given /64 or /48 or even /32 space, and can assign a confidence level that the range is used for VPNs.

IPv6 isn't magically unrouteable, it just routes much larger blocks of "end IP addresses."

You just track and block /24 or /16 as necessary.

Many websites including Soundcloud are still only accessible through IPv4, so this is moot, even if VPNs support IPv6 it's enough to block their V4 exit nodes for Soundcloud.