Since I am tired of time-travel and Barry depressing over his past I would be fine with Captain Cold returning and taking a regular role in the series, and a further refining of his rogues. For instance I am waiting in anticipation for the debut of The Mirror Master in this regard, as he has always been a favourite of mine but very rarely been used to potential or done justice to. I think the television format could put a nice spin on him.
But after two seasons of time-travel and evil speedsters all I ask for is some breathing room from all of that and a developing of the existing cast and settings of Central City.
Well, since Lex luthor is now said to be existing on the Supers Earth, if they do meld them all together as a result of what barry did to save his own mom and that Flashpoint, how about lex sometime in Future forming his legion of Doom from among villains now on that merged earth?