Flash movie is a must.
But you said outside of the usual, Deadman could be cool to see. Granted, I don't know a LOT about him, but from the bit that I've gathered, he seems to have a cool backstory. Plus it wouldn't be the typical, conventional comic book movie plot.
In the same vein, John Constantine could use a reboot (hopefully done better this time). I know he and Deadman are said to be planned for Dark Universe/JL Dark but that doesn't seem like it's actually happening. Not until regular Justice League happens at least.
If Justice League really knocks it out of the park and people really get behind it, a Justice Society movie could be cool. Granted, there would be the problem of how to tackle the "Green Lantern" and "Flash" on that team versus the versions that we'll see in JL, but it shouldn't be a huge issue. A crossover could even happen if both are good.
As far as Batman's universe, I'd like the new Batman movies that are undoubtedly going to come with this new DCCU feature the Bat family extended to the different Robins, Batgirls/women, and partnerships. Even Batman Beyond if we ever reach that point. But to distance the newer Batman from the recent one and the ones with Robin back in the day, it could be expanded into a small team operation with the presence of Nightwing, Batgirl, and Robin alongside Batman.
I don't see characters like Green Arrow, The Atom, the Hawks, or Captain Atom getting solo movies unfortunately. In the context of team-ups we could see them, but in a capacity that Scarlet Witch and Quicksilver seem to be integrating into the MCU. Plus Arrow is already a thing.