I think the Unkindled state was an attempt by the Lords to have a better champion this time around. But as usual, you can be swayed both ways, so the Kaathe team turns you into a DS1-like undead.
If the Undead state was a scheme by the Lords to have humans sacrifice parts of the Dark Soul to keep the Flame going, it was also dangerous, because it makes them more susceptible to the Abyss. The scar on Hollowing bodies is quite reminiscent of the "black goop" we see on Iudex and hollows that turn into Abyss monsters.
Members of the Church were also given a special attire to shield them from that:
"They bore large covers on their backs to ensure that they would not become seedbeds for spreading darkness"
It is very reminiscent of Pilgrims, but we can see that something is sprouting from their back, underneath the stone cover that looks just like the Cleric Set accessory.
It's made of stone and all chained up because I think it's to keep the Pilgrim Butterflies from hatching from them until they've reached Lothric. That's probably why the bridge was taken down, to limit the invasion. It's quite clear that a battle took place.
It is also very reminiscent of Sulyvahn's wings in the 2nd phase of the fight.
So picking a few "chosen" undeads and making them now immune to the curse seems like an attempt at preventing the bad side effects of the curse. I wonder if the whole bonfire creation mechanism that was scrapped was supposed to consume embers. That would make a lot of sense.
As for the nature of the world, I'm more and more convinced that it's not Lordran at a later date. "Where the lands of the Lords converge", which is why there's no need for "teleportation" anymore, it's literally parallel worlds physically merging. Lordran, Lothric, Drangleic, Irythrill and Courland.
