Joachim >> yes, you are right that proposals and designs are different things.
And we already have a namespace for that: Commentary! Good point.
So when a Proposal gets implemented, this should be clearly noted at the top of the Proposal page, linking to the relevant Comentary page (...) The discussion about the Proposal would still be there for those who need to do some historical digging I disagree about these statements. Wiki pages typically don't contain discussions between people - trac tickets do. Unless you meant theoretical discussion of possible approaches to implementing a proposal. In that case, from my experience, once a proposal is implemented most of the discussion about alternatives becomes irrelevant. Of course a good commentary page will contain justification for the design choices that were made so that exploring dead ends can be avoided in the future.
Andrew makes some good points. We don't want to move pages around - we just want to tag their status. That would be a Good Thing to have. Janek