Thanks to impressive fan art, Henry Cavill transforms into Kingdom ComeSuperman from Alex Ross' alternate story, which depicts the character as an older, more jaded hero rejected by humanity for a new age of heroes.
The Snyderverse would have ended in Justice League Part 3, which followed the events of the Knightmare timeline in Justice League 2, where Flash uses the cosmic treadmill to jump back at the correct point in time, leading to an alternate timeline where Batman sacrifices himself for Lois and Superman never succumbs to the anti-life equation. Superman would have led the forces of Earth, including Amazons, Atlanteans, Men, and Lanterns, in defeating Darkseid. This would mark the end of the Snyderverse, but it could have led into its own Flashpoint storyline set up from Batman v Superman, starring Jeffery Dean Morgan as Flashpoint Batman and Lauren Cohan as Joker. There also could have been room for one more Elseworld story to this plot line or even one that exists as a diverged timeline that perfectly sets up the events of Kingdom Come with Cavill's Superman.
Skull101ify posted an edit on Instagram of Cavill's Superman from BVS that shows what the character could look like in Kingdom Come. Rather than adhering Cavill to Ross' vision, the artist envisions the opposite. Superman's black suit in Zack Snyder's Justice League is an alteration of the BVS suit, and the BVS suit is an alteration of the MOS suit. The Kingdom Come suit is similarly created as if it stands beside them as a unique version. The edit goes a step further by not only depicting Cavill as much older to reflect that appearance of the character and storyline but also by using the specific scene from BVS that further mirrors the themes of Ross' Superman existing within a democracy, as shown in Peace on Earth and Kingdom Come.
Brandon Routh wore a variation of the Ross suit in Crisis on Infinite Earths, which featured Kevin Conroy as an evil adaptation of Batman. However, having a story with Cavill as this future version of Superman would have fit perfectly within the themes and tone explored in the Snyderverse. While Bruce Wayne would have died, or more likely, been sent back in time by Darkseid's omega beams, as presumably teased in ZSJL and inspired by Grant Morrison's Final Crisis, Clark and Lois' son was set to become the new Batman 20 years later, which is presumably when this Kingdom Come adaptation would take place.
James Gunn seemingly hinted at Kingdom Come within his 10-year plan for the DCU, but starting over with a younger version of the characters makes far less sense than continuing with Cavill's Superman and having him star in a future Kingdom Come adaptation because his character arc within the Snyderverse would have established him being pushed towards that storyline.
Source: Skull101ify/Instagram