I don't mean to put you off, but the whole engine of Empires will still not suit a WW mod. There'd be no way to represent trenches, a war of attrition rather than occassional great battles. Still, ETW would still be a lot more suitable than RTW or M2TW, and I think WW mods have been attempted on those a couple of times.

As the TW series develops, its getting harder for people to mod anyway. Even if they include tools, graphical improvements and the more complex engine will make modding effectively a lot more complicated for all but the best modders. Modding M2TW is a lot tougher at modding than RTW, and I expect the leap between M2TW and ETW will be greater than between M2TW and RTW.