A universe where none of the major DCU-original heroes took up their heroic identities, and the protectors where all the Fawcett, Charlton, Quality, ect. heroes. The DC characters would still exist but as non-powered supporting characters or minor adventurers like Hal Jordan being a Blackhawk, for example.
A universe that is a take-off on Speeding Bullets and In Darkest Night, where the Wayne's find baby Kal-El and raise him along side their biological son Bruce. After their murders, Bruce helps his brother develop his heroic identity and methods but the brothers have a falling out over Bruce wanting to fight by his side. Bruce goes on to get a Green Lantern ring and forging his own heroic identity. This world would be populated by heroes and villains that take on elements of other heroes like a Diana who is a sorceress instead of a warrior or an Orin who gets a hold of a Nth metal harness that allows him to fly, further augments his strength, and allows him to breathe hydrated oxygen while on land.
A Marvel Universe one I'd like to see is where the Marvel human heroes/villans were born as mutants and the mutants were born as regular humans.