Seeing how this is supposed to be the end of the Dark Souls trilogy, I hope they don't change the ending with the DLC like Dark Souls 2 did. Dark Souls 3 kinda needs to end well on its own seeing how its wrapping up things.
I have a feeling 2 only needed to to tie into Dark Souls 3, though.
I think the broken archstone was cut content, not necessarily intended as DLC.
I red somewhere that they used a lot of it in DS1, mostly in Sens fortress.