IMO ipv6 would have gotten far more adoption had they used a different assignment scheme:
* Turn every ipv4 assignment into an ipv6 assignment by zero-extending to the left, i.e. 72.217.16.142 becomes ::72.217.16.142
* New addresses come from a new assignment ::2a00:0000:0000/96 which contains as much as the ipv4 space. So new addresses look like ::2a00:72.217.16.142. A little bit messier than ipv4, but still tidy mostly.
In fact, this address syntax is a valid syntax variant of ipv6 addresses. These addresses are just not assigned today.
Had we used this scheme instead of the current one with its extremely long addresses, we'd have had far greater adoption than now.
Note: yes I'm aware of slight incompatibility issues between ipv6 and ipv4, like higher minimum MTU values of ipv6. I'm not suggesting a translation of ipv4 to ipv6 here, the hosts would still speak the two different protocols, but the assignment would match the ipv4 assignment.