I get where you're coming from, but the reason I suggest short-chain flails is because it could be functionally similar to the bludgeons already in game. That is, it can use the same animations without any bad side-effects.I still dunno...
The point of putting a ball on the end of the chain is to amplify the amount of force you can put into a swing, but if you make the chain shorter, you lose out on angular momentum, and if you make the shaft longer, you might aswell just use a pole hammer or it just becomes a normal flail. also there's like what... 5 real examples in museums?(possibility that this thing might not of had actually been used in combat often or at all)
EDIT: well I guess theoretically it(ball and chain) could be used as a shield killer if the point is to use the swinging of the ball to hit them from behind while the handle is blocked from the front
A short-chain flail would still be devastating, much more so than a regular mace, to the point that using anything with a longer chain would be overkill for most enemies we've already seen in game. And it could still work against shields if you're skilled with the flail, or lucky.
But, we want to go all out right? Hell yeah I want some crazy room-clearing homicidal wrecking ball on a two handed shaft. But that would require new techniques, new animations etc.