One problem with PvP MMOs is that they can fall into stagnant states. Each major entity has their own empire. The empire generates enough resources to maintain that power. The empires are unwilling to fully engage other empires in war, because there's a chance they might lose. Instead they'll skirmish on the borders to relieve boredom.
In theory, new entities could challenge the existing empires. In practice though, long-standing empires are usually structured better than the challengers. The empires have been around longer, and have seen what works and what doesn't work. If a challenger does arise, they are usually beaten into submission quite quickly.
When you get into the stagnant state, the real threat to an Empire's survival is not other players, but internal drama. It's arguable that Eve Online has fallen into this state now.
Perhaps the problem is the very concept of empire itself. Once an empire is in a steady state, it usually stands until something major changes. Things like the emperor dying or succession struggles. But these sorts of events are unlikely in PvP games.
A better structure for PvP MMOs might be "nomadic tribes" rather than empires. Under the nomadic model, resources in a given area are consumed faster than they are generated. Thus when the resources run out, the nomads must move on to new regions.
That movement brings them into contact and competition with other tribes, making conflict and war more likely and more necessary.
Imagine that all the CFC's territory in Eve Online suddenly stopped producing resources. The CFC would have to move, and that would generate a huge amount of PvP.
But there is an attraction to holding territory, to claiming "your" space. I'm not sure that a nomadic game would have the same attraction that the empire games do.