First, there is very little cost to any large tech company to state a date that they expect to turn off IPv4 for certain services. "To get our free xyz service after January 1, 2028, you'll need to be on a provider that supports IPv6". The tech companies can then push out that deadline if they don't see enough adoption as the deadline approaches.

You’re suggesting they should bluff, essentially - this is great!

There are, of course, risks related to consumers switching to other alternatives prior to the date and also various other reputation and legal risks.

Exactly, which is why this won’t happen until the $$ saving due to abandoning v4 outweighs the risks above.

I guess if one was to abstract the above out at a very high level it would be to say that about the easiest way that I can see to further accelerate IPv6 adoption is to either start to provide certain desirable services only over IPv6 or at least threaten to do so.

Did you consider a legislative / government level incentive? The EU just forced all mobile devices sold in the area to have an USB-C port, why not enforcing a requirement for IPv6 on all broadband and mobile connections?

Or at least a mechanism to clearly identify dual stack broadband offerings vs v4 only?

US is also mandating a v6 support requirement for gov-contracts - why not extending?

Ultimately - the commercial world can create incentives, but lawmakers can enforce.

The Googles of the world just happen to be in the best position to do just that and may have a financial motivation to do so (if they can do so without negatively impacting their bottom line).