The gist is that low level zones and underpopulated areas will be cross server, so for Ravenholdt we'll have every RPPVP server in Durotar for example. This also means that people from all RPPVP servers will have the opportunity to interact with one another in World PvP, RP, and other events.
From what I've seen of other RPPVP servers, I give it less than a month before we gain the reputation as bullies from the other RPPVP servers. The Emerald Dream/Ravenholdt rivalry will no doubt grow, but the other ones barely classify as PvP servers, let alone RPPVP.
It'll be interesting.