It was rumored for like a decade. The last 32-bit computers were sold in something like 2007-2008? High Sierra started throwing warnings when you launched 32-bit apps. In 2018, they announced Mojave would be the last version to support them. Mojave just got an update yesterday and will likely get updates for at least another year. So nobody has been forced out yet.

I'm aware end users with discontinued software were forced into some no-win choices. But as an ecosystem, it's one example where this happened and was given a ~15 year possible window and an explicit 4 year window to transition.

And it couldn't have happened sooner.

Do you want to be burdened with layers of backwards compatibility and end up like POSIX or Autoconf with provisions for things that once run on some long forgotten UNIX OS version?

32 bit support certainly isn't going to Bury you in backwards compatibility. It just runs

Just runs with 2 versions of the same library (32/64), and with older programs that can't take advantage of 64bit ABI / arch changes...