The leading theory from what I've read is that people think Elizabeth has been possessed by the Supreme Deity, all because of her smile which is characteristically very unlike Eli to do (I don't recall her ever making a smile like that before, even as the Bloody Ellie?).
What are the odds its actually the SD? It... could be fitting? I've never believed for certain she's been dead since her graces are still active and if they can revive the archangels, why can't she eventually come back? Perhaps her being ''killed'' was just in a physical sense, and she's been a wandering soul or spirit without any way to interact with the physical world.... until Eli turned herself into basically the perfect (and only) vessel for her by putting herself in a coma. It would be ideal, since Eli's spirit wouldn't be there to fight off the possession.
The timing of it too is extremely convenient, unless that's just Nakaba doing this to encourage Mel to actually do something other than be depressed.... but that smile after coming out of the new Demon King being killed and the destruction of the demon realm.... I'm sure the SD would've loved that.
I don't know if the story can even fit her in at the moment, but not an impossible twist for Nakaba to do, I'm not expecting it though.
Powerful characters will be welcome in this current situation, and yes, DS is not truly dead in practice.
When they saw that the Ten Commandments were alive, Merlin said, "A god doesn't die so easily," and that one day the Demon King would return. Therefore, Meliodas also erased his soul, but this wasn't the case for the Supreme Deity; only her body was destroyed. Furthermore, in the film, she said she saw everything through Elizabeth's eyes, which establishes a connection between them.
In that case, the supreme deity wouldn't be a villain, but rather an ally (or pseudo-ally), since the situation is already bad enough without another villain. If correct, DS would join the heroes against Chaos.
It would be funny if she were redeemed.
