Answering to myself... here's the Wikipedia Village Pump discussison about the proposal. The proposal was rejected (or at least not implemented), since it was thought to produce a disincentive for editing signed articles.
Half a year ago I wrote an article about how to implement Wikipedia peer review with digital signatures:
I wrote some time ago an article about peer reviewing Wikipedia:
I submitted it to Wikipedia Village Pump about six months ago, but at the time it didn't go through to the implementation phase.
The basic idea was that a revision of an article could be peer reviewed, so that it could later be referenced as if approved by the peer reviewers. The idea looks actually quite much like the "flagged" revisions that are now under discussion.