I've given it more thought about having two servers and thought I'd share it. (this is just my own personal thoughts)
Basically for me it's going to come down to whether or not a tribe can attack another tribe on their territory regardless of war status after prelude.
If you are not going to be able to go on another tribe's territorry and attack their members or be able to steal items left in the open, then having a seperate pvp server would make sense to me.
My thinking to this is that both servers are going to alow pvp, however only 1 would allow pvp everywhere.
So what's going to happen in my opinion is the pvp crowed is going to be split, we know the casual crowd is most likely not going to be on the pvp server.
However, pvp oriented players will have to determine whether or not they want open world pvp at all times (pvp server), or pvp outside their tribe zones (current server - if attacking on tribe lands will not be allowed even after prelude.)
IF there was only 1 server, then this scenerio would make sense to me for after prelude and I think it would satisfy both the casual and pvp crowd.
1. You can attack any tribe on or off their territory at any time without the ability to do asset damage to any type of architect structure. This would give defensive structures a clear purpose for defending against raids from other players.
2. You would be able to steal gathered materials that have been placed in bins or on the ground in the tribes territory.
3. You would not be able to steal materials placed in houses or a tribe bank, if that's what the banking system is going to allow. (I don't know plans for the banking system)
Edit: 4. Declaring war against another tribe would have nothing to do with your tribes alignment, sometimes even a good tribe can do things to block or hinder other good tribes.
5. If it's possible to set yourself as a nonwarring tribe then you would only be able to control minor resource areas. Warring tribes would not be restricted, however being a warring tribe is not determined by tribe alignment. Also, once you set yourself as a warring tribe you are always a warring tribe- again I don't know how this is going to work, it is just my thoughts on how it could work if there was only 1 server.
6. The only way to do asset damage would be during a siege, declaring war on another tribe would not give you access to the ability for asset damage. You would only be able to siege another tribe if you are currently at war with the tribe.
Edit: 7. When 2 tribes are at war they do not take alignment hits for attacking each other. (if any tribe is allied with a tribe, the war is shared with all allied tribes) Note, you do not need to be at war to attack players in another tribes territory and you can't do asset damage unless you are currently sieging.
8. A good tribe (yes, a good tribe would be able to be a warring trib, but only against evil tribes) would only be able to declare wars on evil tribes, neutral tribes could declare war on both good and evil, and evil could declare war against all tribes.
9. When the ally feature is added, good tribes would be blocked from an alliance that has an evil tribe in it.
10. If an alliance is formed with a neutral and good tribe, then wars/sieging would be blocked against other good/neutral tribes. This would force neutral tribes that want to war into a Neutral/Good or a Neutral/Evil stance.
11. Trade would be blocked between a good and evil tribe. The only other thing that would block trading is if you are at war with another tribe then no other tribe in the alliance would be able to trade with the enemy tribe.