There are several attempts of the TW community to develop a multiplayer strategic game where factions owns provinces. Each turn, economic actions take place, build up of troops and buildings are ordered, troop movements ordered, result of battle resolved via online matches.

It would be similar to Diplomacy, except that the resolution of battle is based on multiplayer battle result.

However, there is a fundamental difficulty:
On the one hand, the online battle must be fair to be fun. Both side must be approximately equal in strength, otherwise, there is no fun playing them. On the other hand, it is of strategic importance to be able to attack the enemy with overwhelming force.

As reasons cited by others above, I wouldn't see MMORPH-like multiplayer as a better alternative. The turn-base nature of TW on strategic map is easier and nicer to work with.

Annie