Who said the best you can do with MnB, a medieval game, is to create a musket mod? Now let me present you WWII China Battlefield, a total conversion mod of MnB Warband based on east Asian theater of WWII. Rifles, SMGs, MGs, grenades, mortars, even flamethrowers working smoothly and efficiently in the mod. There are 7 classes troops for each factions(rifleman, storm trooper, cavalry, machine-gunner, coehorn shooter, medic and pioneer), you need them all working together to win a battle against human players or waves of AI attackers.
Very fun. A lot of work to do yet, but there is a lot of work done. It is the most estable 'modern period' based mod right now for MaB.