I would love to see some sort of strategic level added to this game. It is an absolutely brilliant tactical battle simulator but how battles are fought, or where they are fought, or when they are fought are all as a result of strategic decisions. The lack of Confederate cavalry at Gettysburg was because of a strategic decision, and Waterloo would not have been Waterloo without the strategic maneuvering that led to Ligny and Quatre Bras.
I think the battle engine itself is good enough to be easily adapted to any scenarios of the horse and musket era, and even beyond, so I'm not too bothered about which continent or time period it moves on to. But having a campaign level strategic map where opponents can maneuver at army, corps or divisional level would add a whole new dimension and put this excellent battle engine into the context it deserves.
I'm not suggesting that it should go in for the sort of Total War micro management of towns, buildings and units. The great strength of the current design is that the gameplay has been well thought out and cut down to key essentials. Similarly, any strategic level should be kept simple but should at least include terrain effects on movement speed, and also some recognition of the need for sources of supply. As with the current game, simple but smart is the key.
Of course, having a strategic level means that you would not necessarily end up with the same battles as actually happened historically. In design terms, I suppose it is all about whether you want to stick to playing historical battle re-enactments (which you can still do) or whether you prefer a more sand box approach.