Recent questions here about inappropriate migrations remind me of an interesting bit of perverse incentive.
If a question closes with migration, it's gone. It will never be seen again unless diamonds intervene.
If a question closes for some other reason, it can come back. Particularly if it's a bikeshed, it's prone to return courtesy of being voted to reopen.
Thus, there's an incentive to migrate bikesheds to p.se. Yes, I try to be a good citizen and not 'migrate crap.'
I don't have an entirely viable counter-proposal, but it seems like this might deserve consideration.