Stats: 

 - Super User : 14 migrations (21% rejected)
 - DIY : 5 migrations (20% rejected)
 - Physics: 4 migrations
 - Math : 4 migrations (25% rejected)
 - SO : 2 migrations

Now, an important point, at least to me, is that these migrations only track those that a diamond moderator saw and approved. That means, and I know this to be the case, there are many many more "rejected" migrations for all of them. Sadly, I can not easily pull statistics on that. 

Looking at this, it might make sense to add at least Super User, maybe even DIY/Physics/Math. I will contact the SE comm team and see their thoughts.