Listening and reading to some interviews Bendis has had on the book, the idea seems to be that in order for the JL to better serve the world it needs to expand its roster and views. Thus it's now a cross generational JL. Black Adam and Wonder Mom being the oldest gen, Bruce and Hawkgirl being the middle gen, and Jon, Naomi, and likely Jackson being the future. Each POV making for a more informed JL.
I'm leaving out Green Arrow, Black Canary, and Arthur because it looks like they're all leaving for one reason or another.