TL;DR Stat cap should not remain "to be or not be" kind of question, but instead become a game mechanic.
The "we require stat cap/we detest stat cap" dichotomy seems to be eternal in H&H. I contemplated on the topic for some time, parts of the coming suggestion were scattered on the forum here and there during the long time. You may like some bits of the whole system and dislike another ones: I'm not pretending the complex proposition will solve old problems and not ignite new ones, as well I'm not trying to say I can see all the consequences, or say something like "this is quite simple, no work at all, J&L probly pull one or two levers lool"; yet I think the whole system would be interesting, providing many various motivations to people to work generally in more sociophil less sociopath way.
1.The basic idea is to have a set of parameters which set an upper limit on character growth but can be altered via in-game means. As I see it, the core set consists of "world soft stat cap", "kingdom soft stat modifier" and "personal soft stat modifier".
2."World soft stat cap" is a momentary "groundwaters level", to which any player can level up without any further elaborations.
3.After WSSC is reached, further leveling is still possible, but there so much discussed "stat decay" mechanics starts to apply: while stat is above WSSC, each day some small portion of it is going to be deduced. BUT WAIT! It not just disappears in vain...
4.The deduced amount splits between 2 pools: some fraction goes to "world pool", some fraction goes to "player's pool". When WP becomes greater than WSSC*1000 (or different multiplier, which can even be another dynamic value like the highest online count in the past 24 hours), WP returns to 0 while WSSC permanently increases by 1, thus shifting "the point to which the civilization has been advanced".
5."Player's pool" works in similar way, only applies to the given character only. It increases mentioned early "personal soft stat modifier", which modifies WSSC relative to the single character. That way dedicated grind master with time finds himself with significantly more advanced stat cap than the rest of the world, but the world itself somewhat advances due to his efforts nevertheless.
6.Kingdoms, in turn, also have some means to modify WSSC for its residents: some structures provide a passive bonus, the "kingdom soft stat modifier". Maybe not just a passive bonus, but taking another fraction from "stat decay tax" mentioned in 3) and 4), in a similar way.
7.When player reaches WSSC*2+all other modifiers, he hits "second cap", after which SUDDENLY his character finds he can not be starving and use his full strength at the same time. From this point the denominator starts to apply to his real stat. The denominator depends on current hunger level. For example, it can be 5 for ravenous, 3 for famished, 2 for hungry and 1 for the rest levels. For example, if at this point the real stat is 1000, and the character is currently "ravenous", then the effective stat (used in all interactions with the world) will be 1000/5=200. So, at this point the player must chose between "modes of operation": either he maintains 300% leveling modifier or operates at full power.
8.When player reaches WSSC*5+all other modifiers, he hits "final cap". The leveling past this point is not possible; hovewer, the possiblity to increase "final cap" for a character remains, it requires performing "the hero quests" involving some monster slaying, or something alike, endgame stuff. Each such quest rises "final cap" by another 5% or 10% or other modifier. From this point of view 12 feats of Heracles advanced his stat caps quite good.
9.Have you ever wondered why when the character dies his ancestor receives only 45% of his mastery? Where other 55% go? The final touch of the thing is when the character with stats above WSSC dies, for the last time his spirit alters the world to be a better place: 5% of his accumulated stats and skills immediately go to "world pool" mentioned in 4); if the deceased belonged to the kingdom, another 5% goes to his "kingdom pool", provided the kingdom has the capabilities at the moment; and after that the spirit not vanishes, but resides in rock or tree, becoming new quest-giver named strictly after the deceased character and providing another 5% to the world. If the vessel of the spirit will be destroyed, that bonus will be lost.