I think it's going to be something pretty deep to wrap up the series, a good vs evil, original sin kinda thing. Just seeing too many clues that feel close to Christian type symbolism: serpents, angel wings on particular mobs and feathers in a weird cage up in the rafters, beings reminiscent of anunaki/Nephilim/giants, light and darkness, dead walking the Earth/rapture sorta stuff. So yeah...maybe all that is just the typical winks and nods to real world mythologies and theologies often found in dark soul's particular brand of mysterious and gothic storytelling, but it is at least possible that it is much more significant and familiar than that...