[Tikuto]

An ordinary blade would be fine with me though maybe with futuristic style but no special features like a chain or a magnetic attraction or even then weird glowing shit that the Vanu had. Just a blade that can be used on its own or attached to weapons, which automatically attachs itself when equiping these weapons. this saves the tedious time of having to select a weapon or having to drag-drop the knife on and off your weapon.

Infiltrator melee
As I've suggested in other threads, allowing most players to have a Darklight vision not as an implant but as a helmet feature may allow for balance prospects for the Infiltrator to be more powerful and more exciting.
The infiltrator suit could have an external bionic that looks like ribbed-worm resting hard on the infiltrator armor supporting the bodily muscles, and would work as "extra muscles" to boost run-speed and melee power like Surge and Melee Boost implant. Where most players will have this Darklight vision available (not as an Implant but as an armor utility) this can counter-act a powerful imbalance, don't you think?