OK, this is off topic to an extent, but DTMF provided the opportunity for immense savings in the cable plant because of the copper gauge reduction allowed. Dropping the requirement for transmitting switch actuations (DC on-off) allowed development of more cost effective transmission solutions. The removal of the mechanical dial and included governor mechanism dropped both manufacturing and maintenance costs for telephone sets and provided the opportunity for creative packaging not limited by the rotary dial size. 

That’s enough off topic for now.

As for IPv6: If one assumes that the Internet is a world-wide network of networks and that connected devices, including multiple personal devices, will continue to proliferate — Management and equipment cost for kluges to compensate for the dearth of IPv4 addresses and still provide universal connectivity will continue to escalate. Investment in native IPv6 provides an obvious future cost avoidance opportunity.

Even ISPs that say, “My network is just fine.” will eventually run into this financial reality.