Honestly, I'd prefer to have to annotate non-exhaustive records:
let { foo = foo; bar = bar } = x
should only match { foo; bar }, but
let { foo = foo; bar = bar; .. } = x,
can match records with more labels.
You're right, that seems way better. The syntax is really much clearer, and I like exhaustiveness as the default. The only problem is that it is inconsistent with the current way the compiler behaves. But if you add the exhaustiveness checking only as a flag, and that flag is turned off by the "...", then you're totally set. That's very consistent with other checks in the compiler, such as checks for unused variables.
I think this is a great suggestion. I'm curious what Xavier thinks...