March column isn't the same as road column. It's still a combat formation. If we were dealing with road column, I'd say you were exactly right, that as bad as line is for security from attack from the flanks, it's still better than road column. And line IS bad if the threat isn't directly in front of you when encountered by surprise, which is how it normally happens. It's no easier to turn a battalion in line to face a threat from the flank than it is to turn a corps the same way. Also, the formation change that takes the longest is from line to square.
You've already got the ability to specify line or column when you give a corp a deploy order, so that part of your request is covered. If you're trying to get the same thing for individual regiments, I'm wondering why you're maneuvering individual regiments enough to worry about it.
Speed is of the essence on a battlefield. If you can move faster than the enemy, you can decide when, where, how and even if combat takes place. If you want to move at the slowest possible rate, go right ahead. It gives me plenty of time to set up a flanking attack.
Troops of any quality can stand in place in line formation, but it takes training and experience to move in line. Lines have to be halted at frequent intervals to keep everyone in line formation. Lines are hard to maneuver, because it takes forever to change facing and still maintain something resembling a line.
Troops open fire at around 80 meters and infantry can see and react to things 500 meters away. It's highly unlikely that you won't see a threat until you're within the open-fire distance. I can't guarantee that it's even possible within the game. If not, it's one of those minor details that need to be added before we worry about trying to model combat outside the Napoleonic period, or even on its fringes.
Hook