The AE and Improve Relations modifier alone hurt you for attempting achievements inside the game itself. That is my problem with the proposed mechanic. It really is just another attempt to punish players who want to blob. It's a sandbox, I shouldn't have to sit there and be like "Oh well, I want to do this achievement and I need this land, but in order for me to get this land I have to jump through x rings of fire first."
That was not what you said in your first post. Your statement (which I replied to) was that Paradox are "effectively making the whole game play tall". The new limit will absolutely allow a non-tall playstyle without any problems. 3500 dev, which is achievable without any penalties according to what Groogy said, is not tall. And that is if you fully state everything and do not build courthouses.
They are also allowing countries in Asia and Africa to have trade companies, which will let them hold even more land without penalties and remove the absurd strategy of moving your capital to Europe in order to get TCs.
World conquest and the WC achievements are a different matter. You probably won't be able to avoid penalties from going over the limit when doing a world conquest, however:
1. I am truly not sure whether these penalties are harsher than the hard state cap and hard corruption penalty from holding too many territories in place right now
2. you absolutely do not have to full-state the whole world in order to do a world conquest. The starting development for the whole world is 17.587. Let's assume this will be increased to about 18.000 with all the new provinces in 1.30. Let us also, for simplicity's sake, assume that your cap is 3.500 by the end of the game, that you do not build any courthouses and that global dev is increased to 20.000 by the end of the game.
If you have 1.000 dev fully stated and the remaining 19.000 dev as territories, you will be at a total weighted development of 5750.
I.e.:
after completing a world conquest, you exceed your limit by 64 % and thus gain 0,64 of the penalties. This is just some wobbly math made up on the fly, but a penalty of about two thirds of those values after doing the most extreme amount of conquest possible in the game does not seem excessive.
And I suppose this discounts the fact that afaik you can do all WC achievements while having all of America and Oceania held by colonial nations, which do not count towards the limit.
It is ok to dislike penalties towards expansion, but a little less hysteria (this is not directed towards you, YeP1337, specifically) wouldn't go amiss here.