Pull Requests in a wiki government are of course the same as passing bills and legislation in traditional governments.

What should the criteria for acceptance be?

And what would the mechanism for enforcement be? A blockchain solution where many nodes have a copy of the law and all nodes must remain in consensus or a law is deemed invalid?

What could be done to make sure that the best answers to legal problems were selected from a pool of candidate answers?

Perhaps people who had the highest number of upvotes on a large number of issues over time would gain some kind weighting such that their policy contributions became more important over time.

Perhaps there are domain specific solutions... Like civil engineers should be automatically given more clout when proposing legislation relating to bridges, etc.