I saw this over in the QoTW, and had a thought I wanted to share for discussion.
My issue with this is not that it's wrong, but that it considers the role of the compiler too narrowly. Many of my favorite writings about rust treat the compiler not just as a transformer of code, but also as a teacher of the community and a communicator between devs about meaning and values.
What that implies in this case is that const fn does two additional things: it assures the programmer that they have written their code I such a way that the compiler knows how optimize it for compile time evaluation (compiler as educator), and it forms a contract between the author and their users that the author will not change the function in any way that makes it non-const in the future (compiler as communicator).
While it may be true that the only thing const fn does in terms of language translation is slow code to be called in const contexts, I think it's valuable to keep in mind the other roles of the compiler, and to acknowledge that const fn has other real effects.