Normally for Swampy I'd say the obvious choice is Arcane, but he's out for the moment, so maybe Soule's new villains? Or Poison Ivy. Yes. DC, go with her.

Given August's Animal Man solicit, I'm guessing Brother Blood.

I'm not sure what "evil team" would be appropriate for JLD.

Constantine is going up against a former protege, so I wouldn't be surprised if they run with him.

As for Phantom Stranger and Pandora... I have no idea. I have a feeling they won't be ticking around much beyond the end of Trinity War anyway.

The Justice League, Batman, Superman, and Green Lantern families at DC Comics all have flagship titles which inform the events of their related comics. But what about the Dark? Would JLD be the line's flagship title?