For a mature product, I think it makes sense to set an expectation of stability - what you see is what you get and if it’s not good enough as-is, don’t use it.
I don’t think closing off all internal discussion of future improvements necessarily the way to go, though? Sharing things like draft standards and programming languages enhancement proposals seems to work out pretty well.
Issue trackers, not so much. I think part of the problem is that the reply box is right there, inviting drive-by opinions, and makes it hard to keep things in perspective.
As the post suggests - the GitHub community discussions are still the place to talk about these items. This is just closing the sometimes literally years old public roadmap posts.
What’s preferable, clarity on what’s actively planned, or ambiguity with dozens of features languishing on the public roadmap without any updates?