We're not going to be opening a migration path any time soon, we don't usually do that while a site is in beta. There is a bit of overlap here, but expats is for people that have finance complications that are intrinsic to living in a country other than their own. In fact, the whole scope of the site is every day life, just with those strange twists that residing abroad can be. There's also a high degree of overlap with Travel SE.
For now, the moderators can coordinate the occasional migration. If someone asking a question on expats is coming at it from the perspective of being an expat, there's probably no reason to send them anywhere else. If someone stumbles into what looks like finance questions there and asks something that has nothing to do with being out of their country, then they'd likely send it over here if it was a good question to begin with.
For the most part, folks that go to expats understand the interesting 'twist' questions need to have, and most things stay there, usually well-received.