Er... the reason that there is no WW1 maps, is because it was boring... I mean, all it was was a bloody stalemate in the trenches. Trech warfare. For how many bloody years. One side rushes across no mans land, attacks the other trench, falls back, and the cycle repeats itself for the other side. Just a giant waste of life, if you ask me. Not remotely interesting to play as an RPG IMO. WW11 was much faster and had a lot of new technology, where WW1 was absically faught on foot and a bit in the air... but the planes were terrible, so there was a very short life expectancy for pilots.
Napoleonic would be cool, especially because naval warfare would be a major aspect.... oh well... wc3 is an old game, and those with fresh ideas like that have probably taken them to other games...