AMD's 300 series is the most energy efficient mobile gpu set yet and we know Apple loves battery power...so yeah.
Source other than AMD marketing? Afaik the m370x is a 270 re-badge and not a new AMD chip and considering how much better mobile maxwell is than the current 2xx AMD mobile I'm not holding my breath. I guess my dreams of a broadwell+gt960m aren't going to happen...
Also, apple is one the few last laptop makers still going with AMD this gen, all the other latest dgpu laptops are going Maxwell.
In other words, we get the same cpu, a dgpu sidegrade, and a new trackpad. Meh