It'd be very easy for such questions to get lost in the flood at Stack Overflow.
Of course, they can be migrated anywhere by flagging for moderator attention. I am curious whether the moderators on this site feel that migration path happens often enough to be a vote target (versus a flag).
We see a lot of content coming from Stack Overflow, because it's more Drupal than programming related. Questions about stuff like Rules and Views.
I can't remember ever sending questions over to Stackoverflow, maybe once in 6 months tops. If we should have a migrate path, Server Fault seems much move obvious since people from time to time ask a question about setting up Drupal on a server. We also see questions about some server config problem with a Drupal site, which isn't related to Drupal, but is a question about setting up Free BSD, linux, Windows or some other type of server.
I've seen a few of those this month, but generally it's quite rare to see questions being migrated away from the site. I don't think we see enough to make it a close reason. In time maybe, but I think it's premature. Especially since questions usually are closed by moderators anyways - not enough high rep users using the close button.
One thing worth noting in this debate, is that migration paths are only needed if the community closes the question and not a moderator.
My feeling is that all questions or very close to all are closed by mods. So this proposal is meaningless if this is true.