When I backed Eternity, I thought the Endless Paths were going to be some end-game deal where, just before the final boss, you can go to the Optional Dungeon(breeding the right kind of chocobo first), fight all the hardest mosters, and at the bottom of the dungeon is an encounter that's harder than the actual end boss.
I don't know what to think of the version we're actually getting. Since it's apparently really big, chewing off piece by piece would make the whole thing easier to digest, but it takes away from the epic feeling if it's not something you seriously prepare for beforehand and then finish in one big struggle.