I'm really in favour of OPs suggestion. Of course the numbers are placeholders but even in their raw state they work pretty well in my preliminary calculations. But there's two arguments to be made here:
Is the suggestion justified?Yes. Each heirloom is statistically only a small bonus, but in some cases that small bonus has a disproportionate effect. A masterwork side sword (MSS), for example, has 103 speed. There are very few weapons, of any generation, that can match that speed. This means that a MSS in close combat is almost unequaled in terms of speed. It's not just a 2% bump to speed, but a massive head and shoulders advantage. The SS moves from being a fast weapon to quite frequently the
fastest weapon on the field. Tactically, this is an incredibly important feature for both a person wielding a MSS and an opponent of one. The wielder, if they're competent, knows that they can spam almost any opponent to death so long as they aren't interrupted. The opponent of a MSS must either play with an exceptionally tactical mind or retreat in the face of the MSS.
The other important case is Goretooth. He's a tank, with 3rd gen black armour over his entire body. Many weapons can't penetrate at all, and those that do often do little-to-no actual damage. If even one part of his armour were less Lordly than the rest he'd be an approachable target. Players could aim for his legs, for example, or even just have a better chance at penetrating his breastplate. As it stands, Goretooth fights battles with many opponents' attack not even registering. This seems inappropriate to me, and a situation to be avoided. Increases the overall price of such expensive gear may open up even the thickest of tin cans to some weakness in their equipment and, in my view, make combat far more interesting than just kicking the can till it stops moving.
Is it feasible? I think so. Vicious made a straw man argument out of the costs which I think distracted from the real merits of OP's case. I think I can respond and reconstruct a proper argument for him:
idiotic propose simply becouse even by heirlooming medium stuff, it become impossible to use it with current upkeep
consider loom a simple sidesword (around 10k) and your shield, another 10k , that become around 27k of equipment. considering that average affordable equip is 30-35k, that leaves to the ppl only 3-8k for armor-gauntlets- helm.
There are two claims here, both of which are erroneous. Vicious claims that medium armour would be impractical with OP's proposed cost increase. Let's take an actual example:
Sarranid Guard Armour heirloomed 3 times gets the same body armour as Transitional Heraldic Mail (52) and it weighs way less. However, even with a 30% increase in cost it's still more than 8000 gold cheaper than Transitional Heraldic Armour. This is a good case of medium armour becoming far more effective yet staying cost efficient. And, as OP said, these numbers are just placeholders.
The 1h+shield example was also flawed. A "simple sidesword" is the best and most expensive 1h in the game. "Your shield," apparently a steel shield (as even a masterwork huscarl would only come out to a little over 8k), is also the most expensive gear available to a 1h. Even taking that into account, I've already reviewed why a MSS would be exceptionally valuable even for its price.
All in all I think OP has a good point. It needs to be balanced, sure, but it's a solid idea. A friend suggested to me that there should be 3 armour-heirloom slots, that are free, but the fourth starts to cost extra gold. Weapons, on the other hand, should start to cost extra from the first heirloom. I'm not a developer so I can't give a very informed opinion on price, but perhaps the additional price should only apply to the highest tier gear? For your consideration.