Alright, here goes nothing!

Basic idea:

On neutral realms you start your char on your normal faction's side for the first few levels. (1-10?)
Then everything is in your hands. You can learn other languages, become neutral to the horde-ally war and build up your own or join someone else's guild based faction. Fight the enemy guilds and make allies with other guilds!
You can be the troll that fights for the argent dawn, you can be the assassin that kills for money, you can be the wild hunter that only trusts his pet and weapons and you can be the blood elf that sticks with the alliance.

How it would work:

Well, the first 10 levels would be basic. Then you can go to a "Faction representative" To become neutral with the other faction and learn the other side's primary language. If you gain friendly+ with every no- longer enemy faction-faction (Stormwind, Orgrimmar, Darkspear Trolls etc...) The reputation with your "initially friendly factions" will start to drop. If you want, you have to declare war with one so it can drop below neutral.

Example: You are an orc that is now honored with every ally faction. You can go to the representative of the alliance to allow your horde reputations to drop down even farer, or you can kill 5 horde NPCs or 20 horde guards for the same effect.

Guild based factions:

If you're the guild master of a guild, you can select your guild's allys. Alliance, Horde, Steemwheedle etc. and of course other guilds. If you want to ally or fight a guild, you need an agreement with the other guild, or else you'll be neutral to them.
You can choose if your guild works like that, or a 100% Neutral setting. Neutral guild members have the same rights type as the guildless "Solos", with the additional +fsolo available to them.

Solo:

Basic idea, Check a simple little box that says "Become Neutral" in your reputation window.
Then a window would pop up that warns you that it will set every reputation back to neutral. You can no longer be friendly with one main faction (Alliance/Horde) without becoming an enemy with the other one. You have to go back to the faction representative and pay to get your reputation to back neutral as this function will only be available once for free.

Example: You ticked the neutral box and accepted the warning. Now you're neutral with every faction you know. Fight for the Horde, it will raise your reputation with it but drop the alliance one. If you don't want to be an enemy of that faction anymore you can pay an increasing, talent point style amount of gold to set it back to neutral and make it undroppable again.

There would be a /solo command that works similar to the /pvp one. Activate it, and ANYONE can attack you if they also have the /solo flag on. Please note that ANYONE can use this, even if you're friendly+ to someone's faction YOU WILL BE ATTACKABLE FOR THEM.

/faction:

Solo flag but your guild/faction mates (People who are friendly+ to 2 factions you're also friendly+ to) can't attack you. You can say this allows you to fight off outsiders.

Assassinating:
You have the "Assassination" possibility every 3 hours. You can find this "Ability" in your spell book. Target someone, cast the "Assassination" spell and it will force the character to become hostile with you until either you or the target dies. Lowbies (1-10) are immune to this and the 3 hour cooldown stops most of the ganking. You can loot a "Mark of assassination" From the target's corpses that notifies you killed him/her. (this is mainly for roleplay reasons.)

/pvp
For all guild/faction relations the PvE ruleset counts to keep the whole thing safe from gankers.
If you /pvp (Only works if you're in/friendly+ to a faction/guild) Everything your faction/guild is against becomes hostile just like in normal servers.

NRP:
Simple: The Neutral ruleset combined with the RP one.

I noticed how much I suck at making things readable and hope that everyone understands my gibberish.

[ Post edited by Thirdone ]

Sounds like fun, but also like a different game from WoW ;)
World of WARcraft on neutral territory.

I'm joking. A lot of people read these forums, so if you ever see something like this, we'll know whom it came from ;)