Jeffrey Dean Morgan, whose career shifted to a more comic book-friendly path after 2009's Watchmen, appeared as the iconic comic character Thomas Wayne for one of his two biggest onscreen moments this year. So it would make sense (in a fanatical kind of way) that the actor could potentially play the billionaire for The Flash's upcoming Flashpoint story arc as alt-timeline Batman. Would he be interested in playing the Caped Crusader?
To the cheers of audience members and the spine-chills of evildoers everywhere, Jeffrey Dean Morgan voiced his support for being added into The Flash Season 3 during this past weekend's Denver Comic Con when asked by a fan. I mean, it would admittedly be ridiculous for Morgan to bring any other genre of response than "Shit yeah!" But still, this isn't like asking him if he'd want to play Bruce Wayne's Batman in a flash-forward on Gotham in Season 5, since he has legitimately gotten into Thomas Wayne's headspace in the recent past. He could do this. And as he said elsewhere in his answer, he'd talked to director Zack Snyder about taking part in a Batman story, so he's been thinking about it for a while.
Would Batman have a mustache in The Flash's Flashpoint timeline? Is that the kind of world we'll live in now that Nora Allen has been saved from Reverse-Flash? One where mustaches are terrifying?
Logic hasn't escaped us all, of course, and the chances of Jeffrey Dean Morgan donning a cowl on The Flash aren't exactly the most likely. But the main thing standing in the way of it, at least outside of practical things like scheduling and story-forming, is that DC is so very much against letting its cinematic and television worlds collide or crossover in any way. To the point where some characters are completely off-limits.
Even so, though, Morgan's role in Batman v Superman: Dawn of Justice was extremely slight, and one would presume that The Flash will almost definitely have to back-pedal out of its timeline disruption at some point soon to bring the status quo back in action. Which means Morgan wouldn't really have to do all that much as Thomas Wayne's Batman to still have a notable impact within the series. Hell, I'd be into it even if he was only referred to as Thomas Wayne, without any blatant Batman references.
It would probably make more sense for the show to use Arrow's central vigilante as a Batman stand-in, at least for ease's sake. But if there's a way to make a clever connection while also bringing a down-for-it Jeffrey Dean Morgan into this universe, then you do it. But you ask him to leave Negan's bat at home, because this isn't that kind of a show.
Check out the end of Morgan's answer below from the Twitter post, in which he lays out the "anything is possible" answer-extension.