Man of Steel 2 involved borrowing story details from his earlier scrapped Superman trilogy. Vaughn pitched the trilogy, along with Kingsman writer Matthew Millar, to Warner Bros. in 2008, but the studio ended up going with David S. Goyer's screenplay instead, and hiring Zack Snyder to direct (and later become the original architect of the DC Extended Universe).
Vaughn started out producing British gangster movies like Lock, Stock, and Two Smoking Barrels and Snatch, before getting into the superhero game with Kick-Ass (an adaptation of one of Millar's graphic novels) and then directing Warner Bros. doesn't have any plans for Henry Cavill to return as Superman in the near future.
Speaking to Rocketman, which he produced, Vaughn offered some details about his and Millar's original proposed Superman trilogy, and said that he would have borrowed some of those ideas for Man of Steel 2. Described as an uplifting and hopeful approach to the character, the planned trilogy would have changed Superman's origin story to have him grow up on Krypton instead of Earth. The first film would have been set mostly on Krypton and focused on Superman's father, Jor-El, as he tried to prevent the ultimate destruction of the planet (though the destruction would eventually have happened). Superman would have only later gotten to know Earth, and would have found his loyalty torn between the two planets.
Of course, it would have been difficult to incorporate some elements of Vaughn and Millar's trilogy into Man of Steel 2, since Krypton was destroyed in Man of Steel and Superman was sent to Earth as a baby, in keeping with classic canon. However, there are plenty of ways in which Vaughn could have made a sequel about Superman being torn between his family on Earth and the people of Krypton - for example, by revealing that the Kryptonian city of Argo survived the planet's destruction, as it did in the comics.
After the backlash to both Batman V Superman: Dawn of Justice and Justice League, Warner Bros. has shifted its focus from Superman to other DC characters. Wonder Woman, Aquaman, and Suicide Squad all have sequels on the way, and Batman is getting a soft reboot in Matt Reeves' Robert Pattinson now confirmed to be taking over the role from Ben Affleck. When we'll actually get to see Superman again - in Man of Steel 2 or otherwise - remains to be seen.
Source: Polygon
