I 100% agree with these rules.
A lot of people (including myself) come from the Battlegrounds 2 community where these rules were used, and they were implemented to keep the game fun and tactical. before these rules were implemented line battles were just a camp fest, that offered little variance in the game play. Musket mod and Battlegrounds 2 are very similar games, so taking advantage of the experiences we had with line battles in Bg2 and applying them to this game simply makes sense. I'm not trying to say that because we played line battles in another game, we therefore have supreme authority, but please consider the experience that went into the making of these rules.
Just because you can't use cover, it then doesn't mean that the two opposing armies just line up in front of each other and just start shooting. The whole idea of the "No cover rule" is to make room for tactics, to make room for manoeuvring and flanking. If you are just going to sit behind a hill while firing at the enemy, then why even be in a line ? it defeats the whole purpose of a line battle.
These are some of rules copied from the battlegrounds 2 Line battle Championship that could be applied directly to Mount&Musket(at least for Line Infatry):
All formations used by either side must be close rank ie: all men shoulder-to-shoulder whilst engaging the enemy in formation.
It is forbidden to crouch whilst giving fire to the enemy unless it is in order to allow the rear rank to fire over the crouching ranks heads.
It is forbidden to purposefully shoot at the commander unless there is no other target presented, ie: if the enemy commander is moving his line directly towards the enemy line and the commander then is killed because the enemy line has got no other target, then it is not considered an offense.
If the commander is killed during the linebattle he must cease to command immediately and a subordinate must take command.
Using solid cover to conceal your troops whilst giving fire is strictly disallowed. If the soldiers are covered any more than to the ankles it is considered cover. Using concealment however is allowed, ie: Using objects that you might not be able to look through but that you can shoot through such as high grass and hollow trees Soft Cover.
When charging the teams are allowed to spread out to an acceptable degree, however it is disallowed to run towards the enemy whilst giving fire and reloading as this is considered a form of skirmishing. It is allowed to kill the commander during a charge if the two teams are close to melee or in melee. (this rule is worded poorly, it was allowed to fire in a charge, just not reloading)
You are allowed to split your force but you need at least 7 people to start a new line and 4 people to maintain a line. If the number of people falls to 3 you must rejoin the other line immediately or charge. you are not allowed to skirmish with a line unless the TOTAL number of players in the team is 4 or below in a 14vs14 linebattle. If the teams are 20vs20 or more you are allowed to skirmish at 5. This means that you can not have two lines and skirmish with one line that has got 3 people and linebattle with another line that has got 4 people becasue you are still over the minimum limit of 4 total players. (this rule is based on the specific number of troops in a Bg2 linebattle, but the idea of a minimum number of troops needed to support a line could still be applied to M&M)
You are not allowed to open fire untill everyone in the line is in formation, however battlefield stress must be taken into consideration
These rules successfully made line battles fun and interesting in Bg2, and I don't see any real issues in implementing them in M&M