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
The interesting thing is that heroku still is so at the top of what it does, as far as developer UX and ease and reliability. It's hard to describe exactly what i mean, but I know plenty of other people agree. Other things do other things better -- but it's only in the past year or two that some things have started to come close or equal.
I don't know what's going on exactly. Those who set up heroku for the first ~5 years somehow did such a good job that they could coast for another 5-10 and still stay on top of what they were on top of.
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