You've gotta go way back on the Heroku Changelog to find anything that isn't a language version upgrade or feature removal: https://devcenter.heroku.com/changelog
It's on ice. As you say it's also not the first time they've attempted something like this.
Eventually they'll get there, but customers should know that's the direction. They'll be users of "Compute Cloud" writing APEX instead of Procfiles someday.
I think the feature freeze happened in 2018