Sometimes you're pleased to find out a co-worker or classmate plays the same MMO as you do, only to find out they run on another server and that in order to play together you'd have to either re-roll or transfer. If you're both in established guilds this makes things even more of a dilemma, since neither of you may want to pack up and leave your established group for someone you may not ultimately play well with.
Server divisions seem to have their purpose, by all means, as I understand they take pressure off the game's hardware, and also allow for more people to use the same name. Not that it seems to reduce the number of "Killer45467"s I encounter. WoW's floating city would have sunk like an over-burdened ship if it was one-server. People would be packed in there like Japanese sararimen on Monday's first bullet train.
Server splitting also allows for different servers to have tweaked settings... PvP or PvE, despite having "RP" servers they actually seem like a moot point to me. I think that giving people unlimited ignore lists, including global (account level) ignore, and an RP chat channel with some sort of automated ability to mute people who chat in it OOCly based off other players requesting it may be more useful. Even if tools have the potential to be abused, it doesn't change the fact that most people on an RP server are nto RPing anyway. Would I still consider having RP servers? Certainly, maybe two of them. i'd want to be able to flag repeat RP breeching accounts from being able to log onto those particular servers, though.
Preventing them from accessing two particular servers doesn't deny them the ability to play, in my opinion, if they still have access to the other servers. To clarify, I support the idea of being able to travel to other servers after character creation. So even if someone rolls initially on a PvE server does not need to pay or re-roll to go to a PvP server, and if after trying PvP for a day or two they decide they hate it... they're not stung again with transfer fees or the like in order to go back to PvE.
I think a method like this would also allow friends who have different preferences to still hook up and play together... without re-rolling etc... for things like holiday events and other social elements. It also considers the boyfriend/girlfriend issue... where by if one partner is an avid PvP player they can do that and "come home" to relax on a non PvP server with their partner who may be more interested in crafting. (I'm not saying which partner is which, my own gamer girl friends were damn blood thirsty)
I don't think this will stop different servers from developing their own "feel", as people will still gravitate and frequent areas where the community suits them the best. They would be more like neighbourhoods you can drive between than completely seperate entities.
So seperate servers but not isolated from each other. I wouldn't have people toggling between worlds where-ever and whenever, mind you. If already in-combat you wouldn't be able to jump, so no cut-and-run bull shit when you've started some PvP... most likely you'd click on a cross-road post or a border gate sign and select to change servers from there.
I'm a huge dork and would likely colour-code the servers based on the type of rules they had. "Warm" colours would be PvP and "cool" colours for PvE. I'll explain the difference between how I see "full loot" and 10% loot, plus explain my take on safe zones after my Rainbow Brite episode passes.
RED: PvP Full loot, no "safe zones"
ORANGE: PvP Full loot, has safe zones
YELLOW: PvP 10% loot, has safe zones
GREEN: PvE Full loot (occurs only if killed in optional PvP)
BLUE: PvE 10% loot (again, cannot be looted if killed by Mobs, only players)
INDIGO: RP Full loot
VIOLET: RP 10% loot
Wasn't that pretty? Pfft.
The only ones who can loot you is the player or group of players who killed you. PvE mobs cannot rob you of items... although I do think an NPC thief should be able to steal per the 10% rules.
"Full loot" means that for those few seconds before you can release and go revive, the player(s) who took you down can pull items out of your bags, or off your body to either dump them on the ground to take their time with stuffing in their bags, or to pocket immediately. They can also completely empty your coin purse. Clearly, this means I don't think it should take too long for the dead to release. Just a few seconds, makes the act of looting a challenge in itself.
"10% loot" means they can only take from your on-person cash, anything you've banked is obviously safe, they can only take 10% of the cash you're carrying. Only 1 person can take the funds, in a party that would be determined by whatever their group loot setting is.
"Safe zones" on an PvP server would merely be areas where you can toggle off your PvP flag and take a break. Major cities, or inns, basically.
The difference between PvE and RP worlds would, I think, mostly come down to chat differences. RP servers would not support City-chat or zone-chat features, no broadcasting "LFG" or the like. Accounts which have been flagged a certain number of times for breech of RP standards would be barred from accessing the RP servers. Such a restriction is no reason to demand a refund if they are a paying subscriber, they still have two other PvE servers they can access so their use of the game has not been denied.