Well, if governments really care about IPv6 (and the previous campaigns to push it were not just about "look how progressive we are"), they'll do something similar to what they've done with digital TV broadcasting :
they would first ban the selling of new devices not compatible with IPv6, then forbid ISPs to advertise IPv4-only connections as "Internet", then ban the selling of new IPv4-compatible devices.
(In a few years we're going to reach anyway the point when IPv6-only connections (mostly in Asia) outnumber IPv4-only devices (mostly in Africa, which sucks because they're the least able to afford an upgrade, but then being forced behind CGNAT sucks too).)
they would first ban the selling of new devices not compatible with IPv6, then forbid ISPs to advertise IPv4-only connections as "Internet", then ban the selling of new IPv4-compatible devices.
(In a few years we're going to reach anyway the point when IPv6-only connections (mostly in Asia) outnumber IPv4-only devices (mostly in Africa, which sucks because they're the least able to afford an upgrade, but then being forced behind CGNAT sucks too).)