So...basically confirmed with the Legends of Tomorrow trailer having a future Vandal Savage declare "I've seen men of steel die and dark knights fall". Given that
spoilers:
due to the existing time-travel shenanigans of Flash, superhumans weren't supposed to show up for several more years anyway - a future in which Barry was point-blank said to be a founding member of the Justice League - |
end of spoilers it's likely that if we get anything like elaboration on this, Superman and Batman just exist a little ways in the future (or, if my own ridiculous theory remains correct, Thawne erased them from history).