I am fervently against the idea of weapon customisation, one of Halo's underlying elements is being able to tactically assess the opponents assets and plan your next move accordingly. Only have an AR but are being pinged by Sniper rounds, try and find cover and gain ground on your opponent. If Custom weapons were brought into the fray then this would be lost, you may think you have the advantage in a situation, only to be destroyed by some armour piercing rounds, or a grenade launcher attachment. To me, that arbitrary style of weapon balancing isn't a feature that Halo should borrow, and is one of the reasons I feel equipment really didn't work well with the Halo sandbox in multiplayer, because you never had a visual indication of your opponents equipment and thus usually felt cheated when they would pop a regenerator and kill you. This also has me skeptical about the armour abilities if they make the transition over to multiplayer.
And as much as I enjoyed OONSK fiasco, it's starting to feel a tad over-baked now.