I am curious, as there's a lot of mature software out there that will never be updated to make the jump to IPv6; is there a way to emulate IPv4 traffic over IPv

I am curious, as there's a lot of mature software out there that will never be updated to make the jump to IPv6; is there a way to emulate IPv4 traffic over IPv6 to support old software? I mean, I guess there is with 4in6 and Tunnel Setup Protocol? But I've not seen it done yet in the real world. I think maybe if some quirky software developer wrote something popular that only worked over IPv6, maybe we'd see a slight uptick.