There are two basic types of melee attack that can be implemented: Secondary and Primary. Each has their own set of challenges when trying to balance the weapons into a game. A Secondary melee attack is common to shooters. This melee attack is always available, regardless of the primary weapon used. It is generally more powerful than your primary attack, and scaled depending on the average length of an engagement. This type of melee can be seen in Call of Duty. A Primary melee attack is common to RPGs. This melee attack is only available when the player has a melee weapon (or sometimes no weapon) equipped. Since this attack eliminates the player's ranged attack ability, play has to be balanced in such a way that those with melee weapons have a fighting chance and can actually approach enemies without always being killed. This type of melee can be seen in Fallout. Halo 2 is a good example of a game with both types of melee. Not only did it have a secondary melee attack that was always available, it also had the energy sword, which was a melee only primary weapon. I can't really say what kind of melee Destiny will have. We know so little about the gameplay, that I'm really not sure what would fit. If they go the CoD route (possibly suggested by ADS), where you cans die relatively quickly (it really only takes 1-4 bullets to kill someone) I would expect a secondary melee attack only. If they go the Halo route, where it takes much longer to die, (there are shields and it can take almost an entire clip to kill someone) they could more easily include primary melee weapons.