Batwoman, cousin of the Dark Knight himself, is coming to the Arrowverse as part of this fall's yearly crossover.
There's been no news related to the CW's popular DCTV series that's quite as big or shocking as this for, well, years. It's been a quiet rule in the Warner Bros. offices that Batman was untouchable. Fox's Gotham got around this by having the series focused on a young Bruce Wayne, and the Arrowverse has, by and large, done nothing but make vague references to both sides of Bruce's life existing in the worlds of Supergirl and Green Arrow. But if there's a show based in the present day DC Universe, there's certainly going to be questions about whether Batman, Wonder Woman and Superman exist there as well, and what stage of their heroic lives they're in. To tease the answer but never actually give it has been the way they've operated.
Even going as far back as Birds of Prey, which starred Batman's daughter, the character has never been fully featured in a modern live action show. Batwoman's inclusion in the Arrowverse doesn't entirely change that, but what it does do is free up the potential for the rest of the expansive Batfamily to make the leap to television with their superheroic identities intact. Characters like Orphan, Red Hood or Spoiler can theoretically arrive in any of the Arrowverse shows, and it would feel completely natural now that Batwoman has established there are nocturnal superheroes in Gotham City.
There are some characters who can never truly be a part of this universe, of course; Jim Gordon has no real reason to leave Gotham, and Robin already has a TV show of his own in the near future. Basically, some heavy hitters probably can't be used in the Arrowverse, but there are numerous second stringers in Batman's corner of the DCU that have compelling stories to tell without the Dark Knight showing up.
If there's any downside to this, it's that it seemingly says that Batwoman won't be having a solo movie of her own any time soon, which may be disappointing to her fans. The Arrowverse and the DCEU have always had a strange relationship where some characters can be used in the shows, but only until they've got a movie lined up, as is the case with Deadshot, Deathstroke and Amanda Waller. (It's still unclear just how The Flash will work around the eventual movie starring Ezra Miller's version of Barry Allen.) That said, Kate is a pretty high tier Batman character and her inclusion indicates that the lines may be starting to weaken, if ever so slightly.
There are a lot of questions still to be answered about Batwoman and her role in the Arrowverse, but even so, her inclusion means something. The Arrowverse potentially has more toys to play with than ever, and considering just how varied and eclectic Gotham is, it's an occasion well worth celebrating.