I know nothing about Midnighter, but is he someone she can reform? I think it's important to show Wonder Woman reforming men, too.
On an unrelated note, I actually wouldn't mind a Wonder Woman/Black Lightning team-up. They seem like they could have similar approaches to life, but with nuanced differences on how to achieve their goal that could be fascinating to watch while also pushing them both out of their respective comfort zones.
I don't think Midnighter would care much for Diana trying to reform him. As far as he's concerned, he's perfect the way he is.
Courtesy of Agent Z:
Infinity Flux Comics on Youtube gave a very brief review of Immortal Wonder Woman. If it were longer, I would post, but it's only about 60 seconds long. In it, they said the issue was "emotional" and "satisfying" and "really good." They gave a strong recommendation for reading it, and the reviewer was a little teary-eyed when mentioning how much she liked it. This reviewer also liked Yara Flor's "Wonder Woman" comic. Let's hope these comics are as great as this reviewer says.
That's what I like about him with Wonder Woman. Her powers were blessings from divinity, his came from science, but they're very similar. Strength, super-speed, enhanced senses, durability and superior combat abilities are almost Amazonian, but heightened to a far greater degree in Midnighter. Yet he and Diana have opposite personalities and stances on violence. There are lots of sources for conflict but also possible agreement as warriors.
He's a different type of gay man that hasn't been seen in Wonder Woman before. He's one with all the stereotypical liabilities of uber masculinity that she was sent to Man's World to remedy.
There's lots to compare and contrast and they can share the same fanbase.