Nor feeling this already- why must we have additional superheroes than just Supes in his own movie? Just gotta establish a whole universe of heroes again. Sigh.
IMHO, the best "sequel" to Man Of Steel would be to go back to Krypton.
What if Jor El cut a deal with Zod. (Instead of turning him down, which also showed the seeds of doubt in Zod's expression, if rebelling as such was the right decision) Clearly the Council was unwilling to evacuate the planet. What if Jor El agreed to join Zod, but only if they immediately evacuated the planet. There were still military forces loyal to the Council, but what if Zod and Jor El combined their influence to convince the rest of the military to pack up, as fast as possible, and try to load up as many essentially supplies and civilians as possible?
Why would Jor El do it? He might be enough of an "idealist" to be willing to sacrifice himself, but he'd have a chance to save his wife's life, and tons of other civilians from Krypton.
With enough people and equipment, basically a giant fleet of ships heading to the outposts, what if that was enough material and personnel to rebuild the outposts and rebuild Krypton 2.0. And there would be an eventual power struggle with Zod and Jor El, with Henry Cavill returning as Kal El, but not on Earth, but ends up like Charlie Sheen in Platoon, a "son" torn between his two fathers. Russell Crowe would have to lose some weight. And everyone would look a little bit older. But as a "multi-verse" story, it allows Cavill to return in an isolated sense. A different "timeline" where this Superman doesn't have to interfere with Gunn's reboot. And in this new "universe", Diane Lane and Kevin Costner can return as leaders of an Earth deep space expedition, that runs into the outpost. That's quite a bit of veteran acting firepower there - Costner, Shannon and Crowe.
Also the conditions can change. The Kryptonians are not super powered, but the humans become that way. Sure it would take some fudging with the premise, but it's an interesting flip IMHO. You can reuse the "world engine" as the core MacGuffin, etc, etc.
I will still hold, even now, that there is a great film about Krypton in the legacy Snyderverse somewhere. And within this isolated Krypton and alternate timeline, you can bring back other actors. If Ben Affleck can sober up enough, he can be like Weyland and fund the space mission. Bring back Colonel SVU as the military team leader for the expedition, etc, etc.
There was such rich overwhelming potential with Man Of Steel. It's not perfect, but Snyder got IMHO a lot of core things right.
Also Lois and Faoru would mud wrestle for Clark's affections. In zero G, of course.