WHAT THE FUCK??!!
So it seems that this will be it own thing. You play as preset heroes, the level change between sessions and has a focus on coop.
I think nightreign is to elden ring what legends mode was to ghost of Tsushima.
A good move in my opinion. With the mangas they showed that they are not scared to make something non-canon.
I often had the thought that they should make a PvP arena standalone. You can choose from all the skills and weapons and such from across the games and balance for that and focus on netcode.