Around 2040s. We’re just recently making progress in getting people to stop saying the current year as two thousand whatever.

Maybe, saying "twenty" isn't enough of an improvement over "two-thousand" to make it worth the complexity. Compare that to "one-thousand-nine-hundred" vs "nineteen".

Also, years less than 10 years ago which are still referenced a lot then require a switch to a different reading convention. This, I guess, wasn't a big deal from 1999 to 2000 because, "twenty-oh-oh" was too awkward and, hey, it's two-damn-thousand!

I did assume exactly that.

When people that actively remember anything before the year 2000, are in the minority.

So I guess this applies to people born in the 80s (and before), so I assume this will be in the 2030s/40s.

I'm starting to think never.

It's too ingrained. And 2000 was a millenium shift. So I expect a new phrase to emerge.

No, 2001 was the millennium shift. The year 2000 was the last year of the decade, century and millennium.

1999 was when the party started, of course.