I think an appropriate add-on would be a cloaking device type. No, I am not asking for an O.P. thing where no one can see you. To prevent a sense of O.P. It should have either a speed reduction when used or when moving fast the person becomes more visible. Users should be visible on radar and will still make sound for detection purposes.
The best time for it would be 3-5 seconds for standard , 4-6 seconds for advanced and 5-8 seconds for Proto. Cloaking would allow Nova knife users to be able to kill enemies through a new means of stealth like they should be used for. Most Nova knife users are rendered useless when spotted by enemies with long/mid range guns, with this as a possibility I would not like it to be abused.
The second idea I had for the button is a way to hurl an extra knife at an enemy.Sure they need to charge, but that's why they will do half of the base damage of the knife. Having this would allow users to have somewhat of an extra range. Draw backs from throwing a knife could be you only have on knife to charge, but It would be ideal that the knives that each tier would have a higher amount of extra knives to throw such as standard 1-2 throwing knives, Advance 1-3 throwing knives, Proto 2-4 throwing knives.
So with all that said please let me know what you think! Is this something with you want to see or maybe you have a suggestion? Leave some comments telling me what you think!