3) Doctor Fate
The great thing about the sadly short-lived Constantine being retroactively included in the Arrowverse is that any characters it featured now have the potential to crossover. One of these that we really want to see is Doctor Fate.
Though this occult-themed hero didn’t actually appear in Constantine, his distinctive golden helmet turned up as an easter egg at one point. This got fans very excited as, though he appeared in Smallville, Doctor Fate is a character with a lot of potential who has sadly not been utilized enough on screen.
[zergpaid]Somewhat akin to Marvel’s Doctor Strange, Doctor Fate is a title held by a succession of sorcerers. He’s also one of the most powerful heroes in the DC universe, which could make him very interesting to watch.
Geoff Johns has previously hinted that a Doctor Fate solo series might actually be on the cards. So perhaps a guest spot on, say, Arrow could set up yet another Arrowverse spinoff show? We’ll keep our fingers crossed.