Personally, I'd be more inclined to have the Legion embrace the vaguerities of Hypertime: there's one Legion in Earth 0's future; but because Hypertime allows timelines to split off and merge back in, that Legion has ties to seemingly incompatible versions of the Superman mythos. That is, instead of having multiple competing future Legions, present it as one consistent future Legion that's aware of multiple competing histories. There's a more or less consistent overall story that the Legion is aware of; but the specifics are fuzzy.