You know, I've been thinking about it and you're right, it's a big job. As well as a whole set of new Allied armies, we would need a lot of maps. I hate to say it but this should be an expansion rather than new scenarios and we should pay for it. It would be a major project for JMM.
I know JMM has a lot of work doing Patches, so it will be a project in the making. There is a lot of new blood and talent around the game now, guys making OOB's and maps, JMM maybe you could utilize their talents.
There are a lot of Brits here now and I for one would pay for a "Peninsula War and Campaign of 1815" expansion. It would be great fun to play MP or PBEM with French and Allied teams.
My dear French friends, you may even get your revenge!!!!!!!!!!!!!