Rumor about how WONDER WOMAN: 1984 brings back Steve Trevor.

Circe?

I had heard it was Hades (which would be interesting) or his nephew (can't think of the name)- who brought souls of the dead to whichever afterlife they were meant for (Heaven/Hell etc.), and that either Hades is offering to bring Steve back, or the nephew has had Steve's soul in his back pocket for a rainy day when he needed a favor from his half-Amazonian niece.

Personally - I feel like IF it does turn out that it is a god using Steve's soul/existence/life to make Diana his (or her) pawn, then it'll end one of the following ways:

1)Steve sacrifices himself in order to keep things in order, such as his own living would mean this god stayed in this world, or having a dead person exist where they shouldn't will endanger reality
2)Diana has to let him go because she can't do whatever it is asked of her (i.e. "Stay out of the way while I start WWIII, and you get Steve back"), so she has to choose the world/mankind over Steve.
3)Due to trick wording, Steve dies all over again. (i.e. "I just wanted to have a chance to grow old with Steve" when Diana can't grow old, or something like, "Usually they grow old together, love each other till death do they part")
4)Steve isn't actually back permanently- he is returned only for the express purpose of helping Diana because there needed to be someone who would unquestioningly by loyal to her and since they couldn't interfere with Zues's stuff to scoop up an Amazon (Though it'd be awesome to see Antiope!), they scoop up the late mortal Steve, and he lives long enough to complete the job, then over the course of a few days he will grow old and die in a heart-breaking rapid-aging sequence.
5)After Diana kills the god who she made the deal with, his/her power nolonger sustains Steve, causing Steve to either disappear before Diana gets to say goodbye (AGAIN- wishing they'd had more time), or again with the rapid-onset of rapid-aging/illness.