The problem is that 99% of home routers can't handle IPv6, so it won't matter if the ISP supports it. This includes routers that claim to support IPv6 but have critical bugs that prevent it from working properly.
Isn't IPv4 a subset of IPv6? So it shouldn't matter if my home router or modem is compatible, if the changeover is done properly. My ISP would do the equivalent of NAT routing with my IPv4 address being part of the IPv6 address the ISP sends out to the world.