Well, it didn't exist in Batarian history, but if present-day is anything to go by, there will still be people who keep using ancient Human techniques. Keep in mind, a normal katana would not be practical in most situations (since they cannot cut through combat armor). If it were something like the Cerberus phantoms used, then it could be an effective melee weapon. However, melee also isn't something you can exactly rely on when everyone has a firearm. If you use something like a tactical cloak or biotic charge to get close, though, it could be a viable tactic in some fights.