2) Future Flash
A highlight in Legends of Tomorrow‘s first season came when we paid a visit to a future version of Star City. It was there that we met an older Green Arrow who had lost faith in his mission, and while it was only one of an infinite number of futures, it was still fascinating to see where the character could one day end up.
In season 2, a similar episode featuring The Flash should be a priority. The Scarlet Speedster’s series has teased his fate on a number of occasions, so getting to see him ten or twenty years from now would be amazing, especially if his status quo has drastically changed by then. There are really any number of ways this could go, and even a future where Barry has died (at the hands of the Anti-Monitor) and Wally has taken over would be fun to see here.