The classic answer to this is Godwyn. There is quite a lot of room in his story. While he kinda has his related ending in the Duskborn Ending, he is still a pretty mysterious figure. You could go the classic time travel route and go to the Night of Black Knives or to just after at the beginning of the Shattering. But such a setting wouldn’t lend itself to an open world, at least in my mind, since you would either be confined or just retread the Lands Between.

I would be interested in a DLC focused on the Outer Gods. Mainly on the Mother of the Gravebirds and the Mother of Truth (Blood-goddess worshipped by Mogh and the Bloodfiends). The Mother of the Gravebirds is probably a Bird like creature because of her children and her envoys who are twin-birds; I imagine her as a giant Phoenix - Fromsoft didn’t have any phoenices yet, right? I could also see a focus on the elements of the outer gods. Only Rot has ever been clearly stated as an element, but maybe also frenzy, verdigris, and blood(?). Also maybe a bit more insight in to the life cycle of gods since they can apparently die like the Lake of Rot, which is just the corpse of a Outer God, or the tomb under the capital, where the three fingers are. We could even find out in this hypothetical DLC the fate of Placidusax’s god (the vessel of the Elden Ring during his Order). Many plot-hooks you can combine in this Stories of the Outer Gods.

I beat the final Boss of the Lies of P DLC. Very cinematic fight. Very fun DLC overall. I usually don’t enjoy tag team fights that much, but this was very enjoyable. Also some really nice voice lines.

I will carve dread into your eyes that will haunt you forever!

This was probably my favorite mid-battle line. Very nice voice acting by Lea’s voice actor.

This weekend I’m probably going to be using the rematch feature to battle the Overseer and Markiona again, since I easily trounced them earlier.