Here's a way to make an alternative multiplayer campaign map without using the campaign map of MTW, you only utilise the multiplayer optiion that allows to play LAN and online.

Heres the deal:
Multiplayers:
You can have as many players as possible, but this may mean a long time before a whole turn is made. Another interesting option is that you may have more than one player controlling a faction. Eg. Steve and Eve decide they want to control the French, Steve deals with all military matters meaning he fights all the wars. Whereas Eve becomes the King of the French and handles all diplomatic and monetary matters. You might have a whole team of people controlling one faction dividing tasks, making micromanagement easier and an efficient empire

Campaign Map.
A moderator will look after the campaign which is an actual map, with all the important cities between 1087 - 1453, it must have no state borders on it to start off with. You might actually print out a map off the internet or draw up a blank map and plot all the important cities. This becomes the campaign map. It is also a flexible campaign map beause this allows multiple players to campaign on it. The moderator must have a map with the appropiate geographical features like rivers and mountains indicated by a certain distinguished feature. The map must meet the consensus of the players involved so that all may agree to the same map being used.

The length of the campaign can be in seasons or years, depending on consensus between the players involved.

A turn is declared by the moderator when the players have all declared their moves as allowed by limitations. Eg. A player may not deploy his army any further than "x" distance, but he can make as many deployments as he wants as long as they are within the limitations.

Diplomacy:
Everybody's complaining about the diplomatic engine in MTW, so this is a way of satifying people.

Players involved can negotiate between other players on terms of agreement for ceasefires, truces, peace treaty, etc, etc. There is no limit to the kind of negotiations that take place. Eg. The Byzantines agree to cede the Hungarians the cities of Nish and Sardica(Sofia) in exchange for a peace treaty of 30 years, etc, etc.

Once an agreement is made, the concerned parties must have a copy of the agreement. Even then, you might have failed negotiations. On purpose or by disagreement.

Treasury:
This is a tricky one. Will come back to that later.

Warfare:
All battles will be conducted online or on LAN.
The moderator must weigh up the situation and decide on the outcomes resulting from the battle. Eg. The Byzantine faction wants to besiege Melitence. The Byzantines succeed in taking Melitene. The moderator then redraws the map around Melitence incorporating it to the Byzantine Empire as the outcome of the victory.
Basically the battles have an outcome which the moderator must decide and inform the combatants beforehand who in turn must agree on the consequences that follow after either a victory or a defeat.
Not all warfare is conquest, raiding is an option. Players must negotiate with the moderator on the appropiate rewards from a raid if it is successful. Eg. A rich region may yield a larger plunder than say a poor region.
Raids are conducted by the player attempting to move in on the enemy territory, if the invaded victim cannot reach the enemy within a single turn then the raid is considered successful. If however, the victim reaches the enemy raiding force in time, a battle must be fought.

Deployment of troops:
Army composition consists of troops from MTW, eg. the Spanish begin with 2 Spanish Jinettes, 3 Spearmen, etc, etc. When the players decide to deploy an army t invade or raid, etc, they must declare it to the moderator. If the defender of their territory deploys their army, its composition must be announced to the mdoerator. So that when battle is joined the combatants must select the army as announced to the moderator.
More than one army can deployed in the field of battle.
If so they must all be declared to the moderator. However, the deployment of each army cannot be controlled by one player, it must have one player per army. SO if two armies are deployed, two players ont he same side must command each army. They can be deployed in different directions.

Distances covered by the armies must be negotiated with the moderator before the campaign even starts. Eg.
Cavalry can move faster than the infantry.
The maximum distance that an army ccan be moved is 3 cm on the campaign map. etc, etc.

This is just a sample. I have nothing to do. Good bye.