This was an idea in response to my answer on Meta hasn't changed at all.
As we migrate questions from Meta.SO (or any other meta) to Meta.SE, those questions will be removed from the original site. So commonly asked questions will get asked again, migrated, closed as duplicate again, and asked again...
Searching before posting would not work, because the question would have been migrated to SE, and not searchable in Meta.SO. Hence the suggestion: all other meta sites (like Meta.SO) should include searches and "Questions that may already have your answer" from Meta.SE. (or any other meta sites)
This could indicate clearly that a question is from Meta.SE, or not and just have the results merged in. (There are pros and cons for each, from ease of development to interfacing issues.) Hopefully this would cut down on duplicate questions that are already in Meta.SE from appearing elsewhere.