I think world domination (which Jake has given up on in this run) will be impossible in 1.8. There will simply be too many provinces to core or diplo annex / integrate in the game's time frame.
World Conquest, on the other hand, should still be achievable for dedicated players, particularly those who are good at getting HRE reforms passed and give themselves the mighty vassal swarm to help them keep fighting.
Three Mountains will remain very, very rare but isn't that as it should be?
I'd bet on Jake rather than Johan and I'd love to see him do it without cheese or exploits ...
Not at all. The number of provinces is a very, very low cap on world domination options. For instance, suppose I manage to have a heavy divided world where the final states are all under 100% cost to annex. In the last years of the game, I go to war (no coalition) and occupy all the land in the world. I can make peace 12 states at a time (2 base diplomats, Dip/Aristo/Esp, Venetian Ideas, HRE, Curia, Embassy, and 3 policies). I make peace from "the outside" in (and perhaps move my cap for faster annexation). With maxed admin efficiency, I can take a huge tally of land, particularly if I farm cost reduction efficiently. Getting 1000% OExt is quite doable for a very
brief period of time (though it murders your computer to deal with the rebel count currently).
Diplo cost can put a kink in things ... but you can also drop down a huge amount of provinces in Europe by using the HRE to insta gain provinces. And we haven't begun to touch the silly stuff - like say releasing the Ottomans as a free HRE state, helping them fight back to their cores, getting shared dynasty, and then letting them suck dry a bunch of Muslim land (with your help) before passing the reforms.
Now setting all this sort of thing up - that is a lot of work for little reward and is likely really, really hard ... but stopping all the ways players can make a mad dash at the end just doesn't work. Anything where DDRJake can't do World Domination, is a game where normal players have pretty much linearized strategy. Pdox would be very, very well served by not having a design goal of stopping DDRJake from doing world domination.