The CW has been building its own DC Comics shared universe for many years now - first with Arrow, which introduced Barry Allen (Grant Gustin) before he spun off into his own series, The Flash. Then, Legends of Tomorrow was spun off from both Arrow and The Flash utilizing characters from each series in addition to introducing new heroes, such as Rip Hunter (Arthur Darvill) and Nate Heywood (Nick Zano). Plus, The CW acquired Supergirl after the Girl of Steel's solo series initially debuted on CBS.
The change of networks for Supergirl made it easier for Kara Danvers (Melissa Benoist) to join in on The CW's massive annual crossover - this year including all four DC Comics series, and earning the network its highest weekly ratings in six years. Given its success, there are undoubtedly more crossovers yet to come (including a musical event planned for Supergirl and The Flash next month), but don't expect one DC Comics series to join the fray: Black Lightning.
Greg Berlanti, executive producer on all four of The CW's DC series, is currently developing a Black Lightning series for Fox with Mara Brock Akil and Salim Akil (The Game, Being Mary Jane). However, CBR is reporting that when asked if Black Lightning could potentially join the Arrowverse crossovers, Berlanti said, "I don’t think so. If we’re lucky enough that that exists, that that show exists, I don’t think those worlds will cross over."
Berlanti is referring to the fact that while the Black Lightning series is in development, Fox has only committed to a pilot order. The next stage is to complete the pilot and send it to Fox for review, then the network will make a decision about whether to order more episodes and commit to airing the series. Fox has so far found success with two other series based on properties that fall under the DC Comics umbrella: Gotham and Lucifer (with the latter loosely based on a character under the Vertigo imprint).
However, both Gotham and Lucifer are incredibly different in tone to The CW's shows - with the closest comparison likely to be Arrow, though Oliver Queen's (Stephen Amell) series has become somewhat of an outlier amongst the relatively lighter superhero fare on the network. Additionally, the synopsis released for the Black Lightning series speaks to a pre-established universe in which the hero returns to fighting crime after time away, which would create problems in continuity for the Arrowverse - unless Black Lightning were to exist on a different Earth in the multiverse.
That said, DC Comics fans would likely enjoy seeing Black Lightning team up with Arrow, The Flash, Supergirl and the Legends team. It doesn't seem out of the realm of possibility - though the cross-network crossover would be more difficult between The CW and Fox than The CW and CBS - but depends upon Black Lightning receiving an official series order. Still, if the tone of Black Lightning is too different from the Arrowverse, perhaps it's best for the properties to remain as separate entities.
We’ll keep you updated on Black Lightning as development continues.