I think the best part about this idea (besides the fact that it is an amazing idea in general) is that it has a ton of art and thought put into it. The only problem I have with it is that, because it is adding so much new stuff, it is altering the base formula of hard mode. Souls being swapped out for cores is a little jarring, and potentially confusing since it is hard to tell on-sight what core is which, and reading the name of the core doesn't always point to the boss you need to kill to get them. Maybe Might -> Wrath and Night -> Greed, but yeah.
Maybe if this does get implemented it will become less confusing after a few hours of goofing around in it, but for now I still think it has a little too much complexity (in the ores and cores) to be 100% ready for the game.
Great work, though. Not saying it is bad. It is actually amazing. Just a little confusing right now.