Has anyone considered making cross specialization cheaper between Edge of the Empire Careers and Age of Rebellion careers which are similar? For example, Mechanics look like they should cross over with Engineers easier. Or even if you have Mechanic:Slicer, maybe making Spy cheaper, since slicer is a spy specialization? And what about allowing other career signature skills if a specialization is in 2 careers?

Nope, not really. I'd just go with the cost of a new specialization as indicated in the books.

If you really want to learn every aspect of what they do on that other side that is similar but different, then you should actually change what you’re doing and the way you’re doing it, and go live, breathe, eat, and sleep the way they do.

Sure, there will be a lot of overlap, but that overlap could be good. And there will be parts that don’t overlap, and that will also probably be good.