The reason why the melee in MM is so good is because by removing superflous attackdirections they put focus and thought into the remaining too, especially when only one is high damage. By limiting the options it creates a deeper depth in those ones that are left. Feinting isn't the dominant thing, as I feel it is with swords, but other things also have a place like chambers, spins and held stabs all of which create an overall deeper and more interesting melee experience than a feint/block fest.
So by introducing multiple attack directions you're just detracting from what made the melee in MM good in the first place. Also The upstab is something that shifts a bit more power the way of the bayonets compared to swords since it opens up more worthwhile and interesting chamber oportunities than before.
Of course the devs should listen to the community, but ultimatly they need to consider to what parts of the community they will listen, because a lot of the times the masses can be won over by proposing something that looks really cool, but they do not realise that it actually detracts from gameplay because they lack the understanding for the metagame.