3. The References To Batman
Warner Bros.' refusal to allow its DC TV shows to adapt and/or reference The Dark Knight has become something of a running gag. Though those restrictions have been somewhat relaxed in recent years, the fact that Fox's Gotham wasn't allowed to refer to Batman and The Joker as, well, Batman and The Joker in its long-awaited series finale highlighted that they are still very much in place.
However, Batwoman's debut has completely obliterated those restrictions as far as the Arrowverse is concerned. After years of dancing around his existence, The CW's shared universe of superheroes was finally allowed to confirm that they do indeed have a Batman when Batwoman's arrival saw the characters of Arrow, The Flash and Supergirl make their first direct reference to the Caped Crusader.
Thankfully, those references will continue into the series itself as, from the trailer, it appears that the pilot will be centred on Batman's disappearance from Gotham. This will inevitably lead Kate into Wayne Enterprises and, eventually the Batcave (which we also saw in Elseworlds) where she'll discover her cousin's Batsuit - and what a fine looking Batsuit it is.
There was a time when the Arrowverse wasn't allowed to so much as mention The Dark Knight and now, finally, we have a show built directly around a member of his iconic Bat-Family. That, in itself, is worth celebrating.