Spoilers below for what we've seen so far from Season 6 of Arrow, so be warned if you aren't all caught up.
The CW's Arrow-verse has never quite shied away from dropping sweet references to characters and locations outside of its multiple shows' respective jurisdictions, but Arrow itself is making one hell of a batty reference in the second episode of Season 6. Oliver Queen invoked the name Bruce Wayne during a press conference, to try and portray the ludicrousness of the images that "out" Oliver as the Green Arrow. The Star City mayor humorously posited Bruce Wayne hopping away from Gotham City to don the Green Arrow garb, and it's a comment that Fox's Gotham couldn't let slide.
I am a sucker for a bat emoji as much as I'm a sucker for social media cross-pollination involving TV shows. But that's not even the only cool thing about that tweet.
The Arrow-verse has gotten to the point where crossovers big and small are a regular thing, so it's a normal thing to see a Legends of Tomorrow hero popping up on The Flash, or for Stephen Amell to make appearances in other heroes' headquarters. But despite all that, we still haven't seen anyone from this set of DC TV shows crossing paths with any other DC characters from series on non-CW networks. That's logical, of course, given the presumed nightmare of legal and licensing issues that would be involved with such an all-encompassing crossover. So for now, the most that fans can expect to get from a Gotham/Arrow team-up is a social media post. And you know what? We still like it.
Because it's still the carrot dangling in front of the horse as far as what could be within the world of comic book TV connections. Neither Arrow nor Gotham (or any of the other shows) have had any characters using Batman's name willy nilly -- Gotham is obviously building up its billionaire vigilante to eventually become the Dark Knight -- but there have been quite a few instances where characters have referred to Gotham's caped crusader with more generic references. Which would mean that Gotham's relatively timeless setting takes place before much of what has happened on Arrow and The Flash. (At least as far as the current timelines go, since both shows have spent quite a bit of time in the past.)
Stephen Amell has a fantastic idea for a Batman homage, but it's not exactly a crossover deal. Personally, I'd be fine if that one Supergirl family that talked about moving back to Gotham, following their run-in with Superman, would somehow appear on Gotham while making future plans to move to National City. I know the different Earths don't make that likely, but who's to say it wouldn't make sense somehow?
Gotham airs on Fox on Thursday nights at 8:00 p.m. ET, while Arrow airs right after it on The CW at 9:00 p.m. ET. Same night, same universe? Probably not, but we're hoping. In the meantime, check out our fall TV premiere schedule to see when all the other new and returning shows will be hitting the small screen.