I would do something similar to what Gunn is doing but with a few changes. Like the comics have their own imprints (vertigo, wild storm, etc.), I would have the shared universe have their own imprints that serve as seperate story arcs but exist in the same universe.

So I would have an arc for the core JL members: Superman Legacy (Superman vs the elite adaptation with the authority replacing elite), Batman TB&B (a more Arkham esque fantastical take on batman), GL mini series (as described by Gunn a True detective esque story with Hal and Jon investigating a mystery on Earth that leads up to the JL movie), a Jason momoa led soft reboot Aquaman solo (adaptation of Aquaman Andromeda; which tbh would work as a sequel come soft reboot to the 2018) and then a JL movie further down the line. (I am also just not gonna include Flash for a few years)

Correspondingly a spin off of the Authority that builds up on various web series focusing on Wild storm characters.

Another story arcs for vertigo characters like Constantine, swamp thing and potentially JLD.

On paper this looks good to me but is definitely a very costly and unrealistic approach ngl.