It is surprising that so many people praise the CK2`s system of "decline" based on pretty much a crappy random roll, and so few people prise the PI game that almost made the things right.
Yes, I`m speaking about Victoria 2.
In Victoria 2, you got some conselation prise, every time you lost a war, and it actually allowed to do curious stuff with your country. You were getting Revanshism if you lost cores, that could give you more strong military, propell more pro-military parties into power, and give you more political power, make your population wish the revanche, and be willing to strengten the country.
You would get militancy and unrest, that would shatter the conservatives, polarise the country and allow for new reforms, new approaches, and eventually, the comeback and revanche.
If you loose some cores in EU3, you will get almost nothing, exept for prestige penalty. In CK2, if your crappy heir colapses the country, nothing really helpfull hapens, he still sucks as ruler, and you still regret that you didn`t killed him before the succesion.
So, in EU3 and CK2, if you lost something, you know for sure, that you would be better without the loss.
In V2, it is different. You lost, but you got new options, that you didn`t had before. So, it is possible, that the loss is not a bad thing, in the long run.
That, this kind of suspicion, is what makes the player accept the loss, and fight up.
That, is what PI would be better developing for EU4, instead of CK2 system, of "you got bad ruler, sucks for you"(that i assume the monarch points system will be, in the end).
The mechanics that punish you in the ovbious way, just because, you did too good, like the aforementioned Administratve efficency are not interesting.
The way too much succes should not punish you short term, but on contray, you should be great short term, but if things are great now, why change them? So the conservatism, pride and prejudice should follow succes.
On the other way, the loss, should open the closed eyes, show that conservatism is not an option, and shift the country into reform and innovation phase.
That is historical, and that would make sure that the loss is not just a catastrophe, but an opportunity.
The things that are needed, compared to V2, is to make the impact less "controlled".
Than, it will be harder to exploit the system, and make sure that player is not all that eager to loose on purpose, as it often happened in V2.