1) Supergirl
As you now no doubt already know, Supergirl will be making the move from CBS to The CW this Fall. That also means that production will take place in Vancouver, making crossovers easier than ever before (a big four night event has already been confirmed).
Regardless of whether the Girl of Steel remains in her own world or Barry’s decision to tamper with the timeline somehow merges hers with the one already shared by him, Green Arrow and the Legends of Tomorrow, the chemistry between Grant Gustin and Melissa Benoist in that brief meeting they had on screen earlier this year should mean that more team-ups become a priority for the show moving forward.
Perhaps we could even start with the introduction of a completely new version of Supergirl in Flashpoint?