I disagree with this characterization. ARCHITECTURE.md is specifically engineered to be low churn, so in this respect it is meaningfully different from other “keep docs” advise.

In practice, I personally didn’t find it difficult to maintain half-decent ARCHITECTURE.md, and I am not at all good with keeping the docs otherwise.

> specifically engineered to be low churn

This is not actually possible. You're kidding yourself if you think such a document is "future proof."

He didn’t say future proof, he said low churn. These two things are radically different.

When doing code reviews, someone will usually say, "we need to update the docs" if it's a big change. If you can't do that now, file a bug to remind yourself, or assign it to the new guy (maybe kidding).