Based on "The question of whether powerpc remains an architecture in the main archive
or moves to ports is one for FTP masters, not the release team."
That would imply to me you can continue to apt-get update upgrade into eternity as long as you're following unstable or testing. They'll just never be a new stable again for PPC. Someday the FTP masters will remove PPC as an architecture, everything ends someday, but thats not the topic of this notification.
There's a process where the release team freezes and grabs a "testing" and polishes it and cleans it up until it feels its a "stable" and that's never happening for PPC again, just too many release critical architecture specific bugs or the autobuilders are too slow or nobody wants to own PPC as a release arch or ...
The people and teams who generate binaries for unstable and testing are not changing their behavior per this press release, this is a release team announcement.
Needless to say this has nothing to do with stuff like online documentation or mailing lists WRT all the "Debian drops support" type of stories. All the release means is unless something very surprising happens you're not getting a 9.0 install disk. ftpmaster isn't rm -Rf ing the arch, nobodies shutting down nothing, etc..
I mostly hang out with the freebsd world but I hung out in Debian world for a bit less than two decades, so I might be a little out of date, but probably not much.