We all know that the melee system in its current state is pretty janky. It's difficult to react in time to block an attack, hitboxes are weird so teamkills are rampant, and spinning is still the best way to win against numerical superiority. This all seems to have made lines less willing to engage in melee before an all charge is called. However, there is another important factor which seriously hampers any attempts at melee: running speed. Currently, it's far more effective for a line to form up and gun down a charging enemy, making them combat ineffective before melee contact has been met. Infantry can only "charge" at a slow jogging pace, so it's very difficult to make contact when charging
I have two suggestions not relating to the melee mechanics themselves:
1. A sprint function
The benefits of this would be obvious: reducing the time to melee contact gives less time for the other line to form up and fire. However, this would likely require a stamina system to be implemented, along with a host of other related features. Obviously, charging and engaging in melee is a strenuous activity, so the survivors of the charging line should receive a debuff after the melee to prevent yolocharging. However, a sprint focus puts more pressure on enemy lines (especially those who are forming up) and better allows people to storm a position, something that will be crucial in the Conquest mode.
2. A 'suppression' mechanic
Any of you who have played Rising Storm will know about the Banzai ability on the Japanese side. In RS, when a group of Japanese soldiers melee sprint while in a group, they all get damage resistance and a speed increase, while nearby enemies get a suppression debuff, affecting hearing, sight and accuracy. While the ability was quite overpowered in RS, I think that a well-balanced version of the Banzai in Holdfast would make melee far more viable.
Even though fixing the melee combat itself is probably more important, I think something needs to change in order to allow lines to get into combat in the first place. In the current system, if a 10-man line charges a formed-up 10-man line, there's a good chance that between 5 and 8 of the line will die on the charge. While it should obviously be more difficult to attack than defend, these figures will lead to static lines, conservative commanders and a focus on defense, which in turn leads to unsatisfying long-range combat.