It's a sub-basement from the perspective of folks for whom this is a second-order dependency. And it sounds like there are many more of them than there are folks that caught wind of this.

Regardless. The common practice is a year of emitting warnings from the software, that the end-user will see. That's prominent and allows package maintainers enough time to work around the upcoming breakage. Six months notice on a mailing list is simply not prominent enough, and it's half the standard year which puts undue strain downstream.