Baring in mind this is just my opinion based on one piece of evidence.
The second villain...
Is...
KALIBAK.
Why you ask? Does everyone remember this:
That's Henry Cavill posing with a "lightsaber". Only thing is, here's all the lightsabers from Star Wars:
So where did Cavill's "lightsaber" come from? Not from Star Wars I'm willing to bet. But there is a Superman villain who carries something that looks like his "lightsaber"
Kalibak. And the "lightsaber" isn't one at all but his Beta Club.
So what about the "Doomsday rumour"? Well firstly it came from a dodgy source to begin with. No not El Mayimbe himself, he just reports what he hears. Unfortunately what he got was a reportably fake script he still believes is true. And the people who claim they've seen him probably can't tell Kalibak from Doomsday.
Kalibak
Doomsday.
So if Kalibak and by extension Intergang are in BvS. Then the villain in Justice League is kinda obvious.
Interesting times...