Well WFRP doesent account the fact that Plate-armor not only replaced chain/chainmail becouse it offered far better protection but also costed a lot less time and money to manufacture. Its the superrior armour on the field of honor or was…when the longbows and later on the gunpowder-weapons were introduced and made armor kind of useless.
Is it realy harder to hide in armor ?
Well you could say so, to balance the far better protection of plate vs leather but ! It dosent mirror reality at all. You can hide in plate as well as in leather if your plate isent polished to be shining silver…if you´d want that (and get a bonus on charm checks i.e) you will get penaltys in hiding.
Is it harder to sneak in armor ?
Sure armor will moste likely give you some disadvantage due that the chain might russel or the plate might make some klanking sounds but leather itselve does that too…its more a "gnrall squish" sound but its there and will give away your position just as fine. Leather armor is just as stiff as metall if you use it as armor. True it will bend provided enough pressure but that doesent mean you can sneak better in it.
So when heavy armor a bad idea ? When you climb or swim ?
Well armor wont hampe you when you climb a tree or a wall if you have enough strengh and endurance, it will drown you though when you try to swim in it.
Armor is tiering you out…it fatigues you fast thats why knights used horses for protection and to get them to and through the battlefields. Many knights died not becouse they were clumsy but so fatigued that they passed out and were stabbed through the helmet. So in general i wouldent give the missfortune dice for all checks but let take the fatigue system care of that problem. I would only go for TO and ST here becouse AG has nothing to do with wearing armor, you arent realy hampered, you can sprint as well as dance in that if you realy want to. If your trained it might be rather simpel but as trained as you want to be it will always fatigue you.
So my idea for a rule would be like that :" If the soak value provided by armor in each rally-step is higher than ST or TO one fatigue for each point it excells your lower physical attribute"
And yes that means a fighter with ST and TO 5 wont get fatigued by platearmor anymore….but maybe a PC with that attributes would look a little like Mr.Schwarzenegger and i dont believe he would get fatigue problems in a fight that lasts more than a couple of minutes.
If you dont like that maybe youd go with: :" If the soak value provided by armo is higher than you of your physical attributes, take one missfortune dice for each point of soak that isent covered by one of your physical attributes, for all checks involving that attribute ( excluding initiative)"
So we got a few ideas lets cook something delicious out of that all right ?