So on the subject of cross-DC PF/DF, from 7.1 onward, PvP rankings will be region wide, and YoshiP further had this to say:

Y "This is not entirely what I want to do [regarding designated “ranked” DCs per region].... Like Ideally you should just match from wherever right?"
Y "But.... I can't say this yet"
Y "We are working on a matching system that involves every kind of content"
Y "As soon as I have more news, I will make the announcement"
A lot of people are interpreting this as "We are working on it, we just can't be fully certain if it is going to work out yet", so I guess it's as good an update as any.