Repair costs and WPF decrease are the cons of heavy armor currently. But as I see many people still use heavy armor, which is something not desirable for the community. Because no matter how much gold it costs and how much WPF it decreases a heavy armored Robocop with a human sized claymore becomes a very very big problem, the claymore moves fast enough, and most probably destroys it's wielder's foes with one strike. However this is not realistic at all, in such an armor it would not be that easy to swing weapons so easily. I have a few suggestions:
1- Decreasing power strike based on chest armor weight (except for lances on horseback):
Formula is, True Power Strike=[Power strike]-[Armor weight/11] (Integer)
So a black armor, which has 29 weight, will decrease 2 power strike
2-Decreasing attack speed based on chest armor weight (except for lances on horseback):
-%8 penalty for +11 weight, plus -%10 more penalty for 22+ weight
So a black armor, which has 29 weight, will decrease %18 attack speed
3-Bonus movement speed decrease based on foot armor weight:
-%5 penalty for 2+ weight, plus -%3 more penalty for 3+ weight
Thus the game will be pretty more balanced and there will be an alternate role as tankers who tend to wear heavy armor and give points to Ironflesh maybe. Which is pretty underused.
Of course this would attract people to rely on items which has 10.5, 21.5 weight and this is something would destroy the rich set of armors we see in game. For that a more detailed calculation would be better. I must confess I did not really work on it. What I wanted is to present the essence of the idea. I leave the hard work to you, you have more experience than me.