[Supermancho]

Branch merge commit message is where you want the meaningful message. The individual commits are more or less noise for the vast majority of developers (half of which are below average). A useful system accounts for the most common case and it's not on the individual commit level.

[Izkata]

You do realize you're proposing "do extra work to prevent the history from being usable for the small percent who use it", right? The squashed history is lost, not hidden.

And those below-average developers probably aren't looking at the history at all anyway.

[Supermancho]

To be clear, I'm implying that a meaningful branch merge commit message is important. That's the change that matters for project history...which may or may not include a squashed history of the branch. The individual commit messages before that are for the developer(s) to manage as they see fit.

At any time, a developer might make another branch, then merge branches or squash the whole history of their branch or create a new branch and add the changes as if it was a fresh branch. Meaningful history is lost in those cases as well. Adding micro-managing process might get (more or less) predictable results, but it almost always pushes developers toward anti-patterns ensuring those predictable results are not what was intended.