They should have Bow and Arrows. Essentially the same as a gun, except with a different attacking animation, with you pulling back the bow and launching an arrow. I'd be happy if they just did that, but i also have other idea's for the bow and arrows if you want them to be different from guns :
1. You can mix and match different bows with different sets of arrows. So instead of having a bow that deals poison, shock or whatever, you have different sets of arrows that you equip to your bow. So you could have a bow that deals light damage but fires quickly with poison arrows equipped, or a bow that deals heavy damage but fires slowly with poison arrows equipped. This would allow for a lot of diversity.
2. If you get right behind an enemy with your bow and arrow charged, instead of shooting them you pull an arrow out of your pouch and stab them with it.
3. People with bow and arrows cannot equip shields. This would be there biggest downfall, but with being able to do the 2 things up top that guns can't do, i think this would be worth it.
Two-Handed swords. The same as a sword, but deals much more damage and are generally slower than other swords in attack speed. You cannot equip shields, but pressing the button you would normally to raise your shield raises your sword in a defensive manner. Blocking with two-handed swords will generally not be as effective as using a shield.
Dual wielding. The ability to equip a set of two daggers ( not swords ) in place of your shield. You can not mix and match different daggers. You may use a set of two poison daggers or a set of two shock daggers, but you cannot mix them to create a set of one poison dagger and one shock dagger. Daggers generally deal light damage but have very high attack speed. General Charge attacks perform a light spin attack, not knocking foes back to much. If you use a charged attack near a single enemy, you stab them for massive damage like the bow and arrow, except stronger than that. People with daggers can generally move a bit faster than other players. Pressing the button you normally press to raise your shield will instead raise your daggers in a defensive manner. Daggers are very weak when it comes to blocking, they are weaker than a two-handed sword in defense.
This are my sucky ideas that people have probaly posted already, but i thought i might as well.
Yes, this a totally new concept no one has ever thought of before. I applaud you creativity that is superior to all others.