If I had to guess as to what the plan for the DCU is, I'd wager Gunn is going for something freeform. The MCU started with a bunch of heroes in their own little worlds that coalesced into one grand story with a definite end. and then they kept going after that end and fucked everything up.
Superman is being billed as the start of the DCU, but it's not. It's the first movie, but we've already had the animated Creature Commandos show and Peacemaker is getting folded in as well. And there's a possibility Batman and the Penguin spinoff could become a part of it too.
What I think we're going to end up with is a bunch of stuff that's all in the same universe and may share characters but is mostly standalone. This could take the pressure off audiences to do "homework". You'd only need to watch the stuff you're interested in. But the more you watch, the more you get out of the various connections.
We've only had one cinematic universe that could be considered successful despite the many, many attempts. If the DCU can do literally anything that isn't exactly what the MCU did, and make it work, it'll cement itself as something worth experiencing.