Who would LOVE to see John Constantine, portrayed by Matt Ryan, obviously, in season 2 of Titans? He’s got the magical background to deal with Trigon, he’d be a great tie in to incorporate the arrowverse into the dc universe, plus multi platform crossovers would generate more revenue for dc, especially if dc universe allows the crossovers to be aired on the cw, introducing the characters much like they did with him and bat woman (and anyone who saw arrow’s final season trailer, red hood, I think). Or Zatanna. That would be cool, too.
I think the last thing Titans needs is more characters.
I wouldn’t object to seeing Dr Fate have a quick appearance in Titans or DP. I think he would fit better into DP.
We had a tease in the Constantine series as the Helmet of Nabu was an artifact in John’s safe house in Atlanta.
I think it would be fun to see him, but realistically I can’t see it happening. And if he actually was to appear in a future season of a DCU show I would think Doom Patrol would be a bitter fit.