Living in a post-Crisis Arrowverse, Batwoman reveals that there is still plenty to learn about the rules of Earth Prime when it comes to travel between alternate universes. During last Sunday's episode, a confrontation between Alice and her parallel counterpart, who never went down her path of trauma and abuse, revealed some new information on the rules of doppelgangers within this new Earth. Namely, that within the new status quo, as Beth puts it, "This universe is literally not big enough for the both of us, and the longer we coexist in this world, the more we’re living on borrowed time except we’re borrowing it from each other."
Because of this new rule, when doppelgangers share space within the same dimension, each one begins to slowly die as they begin to deteriorate on a cellular level. Their only options are to either send one away to another dimension or kill one to prevent the other from dying. While this revelation drastically changes Batwoman going forward, in regard to the once-sisterly bond between Kate and Alice, this episode also serves to place a new rule within all of the CW's shows moving forward.
Looking to the future, this rule clearly has a greater impact on some shows more than others. While Legends of Tomorrow has revealed some encounters with the multiverse in the past, it appears unlikely that any of the Legends could find themselves in this situation. Outside of the fact that the Legends are primarily concerned with time travel, there has also been a distinct lack of alt-universe versions of the wackiest team in the Arrowverse, with the exception of a Superman from one reality with a familiar face.
At the same time, Supergirl has served as the most affected show following "Crisis on Infinite Earths," as she continues to adjust to the challenges of adapting to a new world and history. In this new status quo, Kara has found all of her friends and family transported to Earth Prime as new additions to this universe. Because of this, it would appear unlikely that Kara would be facing a similar moral dilemma.
Of all the CW shows, Black Lightning's status as one of its more grounded shows has often kept it away from the craziness of the multiverse. It wasn't until the red skies of the Anti-Monitor that Jefferson Pierce found himself introduced to the concept of other super-powered heroes. While it appears unlikely that Black Lightning would begin to lean heavily into the concept of the multiverse, even as he serves as a pivotal hero of Earth Prime and their Justice League, there remains the opportunity for the show to continue building on the dark visions of alternate realities that Jennifer Pierce witnessed during Crisis.
While Arrow may be no longer running, the potential spin-off, Green Arrow and the Canaries, could pick up on this sub-plot as one of its characters remains as one of the few visitors on Earth Prime from an alternate dimension. While in the future, the Laurel Lance of Earth Prime remains the former villain that hailed from Earth-2. While this has held other consequences, there is always the opportunity for the original Laurel to return, or another Laurel to also land in this dimension.
Finally, the CW show that will be affected the most, The Flash, has always been at the center of any multiverse troubles. Namely, this new rule appears most directed as Harrison Wells, as each season has consisted of a new Wells joining the team. Going forward, it would seem that fans can count that any Wells that appears will have to be either sent off to another dimension, or killed, before another can take his place. At the same time, with all dimensional travel stopped, this new rule also serves as a way to prevent other doppelgangers from joining the show, which may fall in line with the show's current strategy.
Regardless of which shows pick up on this thread, it appears that the rules of dimensional travel have been severely changed. As this adds to the complexity of having characters meet other versions of themselves, time will only tell how long this will serve as a fundamental rule of the Arrowverse, and where it will show up next.