The Arrow-verse is getting batty in the 2018-2019 TV season thanks to the introduction of Batwoman in the big multi-show crossover. Batwoman, a.k.a. Kate Kane, has never been adapted into live-action before, and she's already in the running to headline her own show on The CW. Basically, her introduction in the crossover will be a very big deal and could be the start of something revolutionary in the Arrow-verse. None of the current Arrow-verse stars have even been to Gotham City, let alone met a hero from it! When asked about the upcoming arrival of Batwoman, Arrow leading man Stephen Amell had this to say:
Stephen Amell's enthusiasm for Batwoman is to be expected, especially since the Arrow-verse wouldn't exist if not for the success of Arrow. His praise of Grant Gustin and Melissa Benoist of The Flash and Supergirl is no surprise either. The comment of note comes at the very end, when Amell mentioned a character in the crossover "that no one knows about yet" and gives fans something to speculate about while we wait to meet live-action Batwoman.
Now, DC Comics has a vast library of characters, and the Arrow-verse has proven with people like Felicity Smoak that original Arrow-verse characters can play essential roles to DC shows, so it would normally be difficult to narrow down a list of characters who could appear in the Batwoman introduction episode based on Stephen Amell's relatively vague comment. That said, he didn't say that this was a character who had never appeared in any of the shows of this superhero universe, and it just so happens that there's one person who could provide the perfect way to bring Batwoman into the fold. That person is none other than Maggie Sawyer.
Arrow-verse fans know Maggie Sawyer from her role on Supergirl, where she was a kickass cop in National City and very nearly Alex's wife. Kate Kane is a lesbian in comics lore and will be a lesbian in the Arrow-verse, and it would make sense for heroes like Green Arrow, Flash, and Supergirl to welcome a new hero into the fold if they had a familiar face to vouch for her. Kara at least knows that Maggie is somebody to be trusted, although things could be a bit awkward with Alex if Maggie is romantically attached to Kate.
Maggie Sawyer has been a love interest for Kate Kane in the comics, so a relationship between the two wouldn't come out of the blue for comic fans. A Supergirl executive producer recently had positive things to say about how Kara and Alex would react to Batwoman, so maybe any awkwardness would be short-lived.
Kate is described as somebody committed to social justice in Gotham City, so she and Maggie could have a lot in common as law enforcers, just as Maggie and Alex did. Floriana Lima left Supergirl as Maggie Sawyer, but why couldn't she reprise the role to introduce Kate Kane in the crossover? At this point, it's worth noting that the Maggie Sawyer who could be romantically attached to Kate Kane doesn't have to be the same Maggie who nearly married Alex on Supergirl. Maggie could very well be another character with a doppelgänger on another Earth. In fact, she could be the Maggie of Earth-1 who introduces Oliver and Co. to the Earth-1 Kate Kane, allowing the Batwoman show (if ordered to series) to potentially cross over with Arrow, The Flash, and Legends of Tomorrow without hopping universes like Supergirl.
There is no confirmation that Batwoman will fight crime on Earth-1 or Earth-38; perhaps a Kate Kane from Earth-47 or Earth-29 or some other Earth could turn up on the show. Just because Gotham City and Bruce Wayne exist on Earth-1 doesn't mean Kate Kane has to operate out of Earth-1. Perhaps she could live on an Earth that doesn't have a Bruce Wayne at all, which could at least prevent viewers from spending episode after episode wondering if Batman would show up.
An alternate Maggie introducing and vouching for Kate Kane could minimize any drama between Alex and Maggie and get the action going on the crossover, which won't actually involve an episode of Legends of Tomorrow this time around. We'll have to wait and see how the Arrow-verse handles Batwoman's introduction. If she turns up via an introduction from Maggie in the December crossover, I reserve the right to brag that I totally called it way back in July.
Like Stephen Amell, I'm quite curious about who The CW will cast to play such a significant role as Kate Kane/Batwoman. All eyes will be on her to see if audiences are willing to tune in or if factors -- not the least of which is potential superhero fatigue -- keep them from starting the series. If one thing is certain, it's that launching in the big crossover can only be a good thing. Although Black Lightning did well enough on its own without existing in the Arrow-verse and getting a ratings bump courtesy of the crossover, the other shows have enjoyed higher crossover ratings. Batwoman will undoubtedly be seen by plenty of people thanks to the crossover, perhaps giving her exposure to folks who may not have tuned in otherwise.