I don't think the success of IPv6 as a whole hinges on these residential ISPs. I think there is enough momentum for IPv6 already (mobile users especially) that we get a healthy coexistence of IPv4 and IPv6, where new stuff gets designed for an IPv6 fastpath and limited support for IPv4 legacy shims for the "long tail" of adoption.

I guess the ISP space isn't competitive enough that they will ever go "looks like our ipv4 users get shitty latency and more congestion on facebook than the competitor's ipv6 users, so we're gonna upgrade next year!", but their IPv4 setups will probably eventually succumb to attrition too and be replaced by IPv6 gear.