I don't know if it's changed or I just have some issue, but I NEVER see anything but the meta group for a migration option, and the meta group is usually not a good option when I think of migrating.
I would suggest a migrate options list that is sensitive to the reputation of the person suggesting the migration ON THE SITE THEY SUGGEST MIGRATING TO. I have certainly seen high-ranked moderators on site A who know nothing of the culture on site B send lousy migrations. Someone, even someone with a rep of 101 on site A, who is a 3K, 5K or 10K rep on site B is going to know that "this question belongs on site B", and should be able to suggest that, easily and sensibly. That should cut WAY down on rejections, and ALSO cut way down on questions that are closed because there is no sensible way to suggest migrating them where they need to go.
"You can submit a custom flag" Well, no, you can't, FROM THE MIGRATION page. You SHOULD be able to make a suggestion on the migration page, but you can't, actually. You have to take 3 steps back and wonder how much you're wasting your time by making a generic "other" flag to suggest a specific thing (migration) for which there is already a (mostly broken, IMHO) work path.
The current number of migrations completely fails to capture the questions that are simply closed without even a migration attempt, when there might have been a good place for them to be answered.