I wouldn't be totally surprised if they did some steampunk or dieselpunk thing.
I hope not. I talked before about my fear of oversimplifying the story, but this would be the opposite: overcomplicating things. Having Confederate tanks, death camps in the South, and both fascism and socialism in America speaks for itself, and should be enough to intrigue people. If anything, adding sci-fi technology would probably scare off people who decide "oh, I thought this was a serious story, but this is too nerdy for me."
I've been trying to get my family and friends into Alternate History. I even just gave my dad my copies of the TL-191 series books (he likes history, and in particular, he's very interested in both the American Civil War and World War II, so I sold it to him as "why not have both at the same time?"). I might let him know about this adaptation, but I think he'd prefer one that stuck to realistic tech. For people who aren't sci-fi fans, more realistic PODs and stories are an easier introduction to the genre, imo.
Personally, I think they would avoid the whole "US allied with Germany" thing so as not to have what they perceive as negative connotation. They might simply ignore the rest of the world (not that hard a thing considering how turtledove wrote it) and simply have North vs South....
.....WITH TANKS !
It is likely that they'll just stick to America, but I hope not, tbh. One of my biggest dissapointments with TL-191 was that Turtledove didn't talk
enough about what was going on in Europe. I thought there was a lot to explore with the idea of a Europe with a victorious German Empire, a surviving Austria-Hungary and Ottoman Empire, a Russia where the Romanovs manage to cling to power, Action Francaise France, and a fascist Britain. I don't think it would hurt the films to include some details about these events and what the culture is like across the Atlantic with this scenario. The focus should remain on North America, of course, but, like I said, it wouldn't hurt.