Every site in the .SE network have Three "custom closing" reasons, where migration may very well fit. In our community we have decided that migration isn't the priority here. It was decided with the question So, what exactly is off-topic for UX.StackExchange? posted in June last year.
The migration option is a strict moderator activity, which can be hard to find by some moderators at other sites. See How (not why) do I migrate a question to another site as a moderator? for reference :-)
Being a mod at SharePoint.SE i finally got help to notice what could be migrated, and how to do it. The dialogue looks the same here (except from the site itself).
Questions younger than 60 days have the little search box which makes it possible to search for any other .SE site and select that one. But migration should be handled with care. And if in doubt, don't migrate.
So what do we do? Personally I post a close vote as off topic, either by the options predefined, or write my own custom close reason. After that I flag for moderator attention with the simple words "Migrate to GD.SE?". When a mod see the flag, he (there are only he-mods here) uses the dialogue above to post an imediate close and migration request (if it's a valid flag).
And for this extra work, you finally end up with a Marshal badge :-)