I don't think that will ever happen... Too many big businesses squatting on their IPv4 allocations to ever want to spend the money to implement IPv6. They don't need to worry about allocation running out or charging for IPs because they've got theirs.

They would need to be forced to move by customers, probably through an ISP being IPv6 only. And that probably won't ever happen as the customers of those ISPs would drop them for one that does support IPv4 because they expect access to the same big businesses mentioned earlier.

I think the whole thing has lots of inertia to not move to IPv6 and there's no incentive to force it.