I tend to agree with Ewoks. Another point he made the other night that I agree with is that the RvR areas were specifically designed with RvR in mind for the purpose of focusing RvR activity in those areas. If people are able to invade the other faction's PvE areas, they're likely to spend a fair bit of time there. And if they're there and not in the RvR focused areas, when I go out looking for RvR, nobody's there, because they're too busy griefing in my PvE areas instead.
Between scenarios and the open RvR areas, there's going to be PLENTY of RvR going on. But I want to know that when I go looking for it, I'm going to find it in areas conducive to RvR. Heck, I spent hours on end in the lowest tier RvR area in the Empire/Chaos areas a couple phases ago, just because it was so well designed. It's an abandoned town with objectives all over the place, areas for open field RvR, areas perfect for ambushing an unwary party from the other faction, pathways for mounting flanking actions, etc.
I'd rather know that I can find consensual RvR in areas that I know it's going to be insanely fun than have to dodge the zerg just to go from point A to point B because the other faction can exploit geography in areas not intended for RvR.
I'm definitely leaning towards a core ruleset server over an open RvR server.