At the end of the
DC's Legends of Tomorrow finale ... the guy from the other timeship introduced himself as a member of the Justice
Society of America. That brings Earth 2 directly into play for the Legends team (it was already part of the extended "Arrowverse" but not directly broached in
Legends). As mentioned above, there have already been advertised crossovers between all four of the CW's DC properties (they'll have Supergirl in the fall).
Well, we saw on the last
Flash how Zoom escaped at the last second. Should Zoom survive the
Flash S2 finale, they may be setting up for a whole mess of heroes from different shows to converge on Zoom & his crew on Earth 2. Mention of the Justice Society is especially interesting, because they have a guy --
Hourman -- whose powers are direct counter to Zoom's.
They could have really interesting storylines on the CW DC shows with Hourman, because he's both been a Justice Society member and an ex-member. Hourman could be a morally ambiguous character, as he can effectively counter both Zoom's and Flash's powers.