I feel like I've been on a lot of projects that kinda blew up (in a bad way) at the end, and the PMs seemed surprised. But it was kinda predictable, to all of the devs, in a vague way. And there wasn't a great way to raise these vague concerns _during_ the project. :/
I think honest 'feelings' feedback from dev teams up to PMs could help. Track responses, see if confidence is trending down -- if things look bad, at least PMs know there's a problem.
Let me know what you think!