IPv4 is going to be a necessity for many many decades no matter what Microsoft do. Even when IPv6 is at 99%, people aren't going to want 1 in every 100 people to not be able to access their site at all. It'll need to be like 99.9% before we start seeing serious IPv6-only services.

I don't know what the percentage would be, but we do have some historical precedent that could give us a clue.

Best one I can think of is when bigger websites started actually dropping SSLv3 and TLSv1.0 (and later TLSv1.1) support, cutting off older browsers and operating systems. Google and Amazon still support TLSv1.0, but plenty of others (including Microsoft) have dropped 1.0 and 1.1. HN itself doesn't accept 1.1 anymore either.

Then there's browser support. Lots of websites - big and small - cut off support for Internet Explorer 6 when it was somewhere below 5% marketshare because the juice was no longer worth the squeeze. Of course, few of those actually fully cut off the ability to browse the (now broken) website fully but it's a datapoint suggesting trade-offs can and will be made for this sort of thing. Or to put it in the present: a significant amount of webapps don't support Firefox (3% market share) to the extent their product is completely unusable in it.

Sure, but the implementation in the public clouds is totally backwards.

What they should have done is have their core network default to IPv6 with IPv4 an optional add-on for things like public IP addresses, CDN endpoints, edge routers, VPNs, etc...

Instead, their core networks are IPv4 only for the most part with IPv6 a distant afterthought.