#1 Superman – Ultraman
Forget the warped, almost accidental evil of Bizarro, Ultraman is a straight-up evil version of Superman from an alternate dimension known as Earth-3. He has all the same powers and a similar look, but a completely different name. The Flash has already introduced Earth-2, so a visit to Earth-3 in the future would not be far-fetched.
#1 Batman – Batman Beyond
Forget about the modern Dark Knight. Batman Beyond is a new version of the character from the future. Since Legends of Tomorrow involves time travel, a glimpse of this Batman could possibly happen. What makes this version more likely is that it’s not Bruce Wayne in the Batsuit – it’s his protege Terry McGinnis. Batman Beyond would also fit well with the techy aspects of Legends of Tomorrow, as the Batsuit has a number of ability-enhancing components like flight and strength augmentation. We’ll just have to wait and see.
The Bottom Line
Chance are, we won’t see Superman or Batman on The Flash or Legends of Tomorrow. But Legends of Tomorrow does hint that these characters exist, at least in some alternate timeline or dimension. And there are plenty of possibilities for CW to work with if they want to include some alternate version of these characters in the future.