Before The CW's Supergirl has even aired its final episode a new report suggests that the DC Films version of the character, played by Sasha Calle, may be getting a TV series of her own on HBO Max. The big twist here is that the TV series, if it happens, is said to be replacing the long-rumored Supergirl movie, which would have been exclusive to HBO Max, just like what is happening with a number of other DC heroes like Blue Beetle and Batgirl. Apparently, the character will be introduced in The Flash with a good deal of mystery surrounding her, and the show will aim to give answers.
Per That Hashtag Show, the series would star Calle and likely feature at least a guest appearance by Michael Keaton's Bruce Wayne/Batman. Superman, on the other hand, would not appear, although it's possible other Kryptonians might.
The report suggests that the transition from movie to TV series was a result of script rewrites, which ultimately suggested the creative team needed more real estate to tell the story they wanted to tell. If true, that would certainly be an interesting path to development for a project so high profile, but in the ever-changing streaming economy, it doesn't sound unbelievable.
The series would likely be significantly different from the Arrowverse Supergirl series, which centered on a fairly traditional version of the Kara Zor-El story. Superman's cousin was sent to Earth to watch over the infant Kal-El, but was knocked off course in hyperspace, and due to relative time, arrived decades after, now physically appearing younger than her cousin, who is already a global icon.
Sasha Calle's portrayal of Supergirl in The Flash is said to be partly based on the character of Cir-El. Created in 2003 by Steven T. Seagle and Scott McDaniel, a human/Kryptonian hybrid with a myserious past of her own, who initially showed up claiming to be the biological daughter of Superman and Lois Lane (this was later revealed to be untrue). It is not known how much, if any, of that backstory will inform the character, or whether it's just her physical appearance that will tie her to the "alternate" Supergirl.
If true, the rumor seems to suggest that Warner Bros. is viewing the comparably inexpensive TV projects on The CW as something of a proving ground for concepts that can go "bigger" on HBO Max and in theaters. In addition to The Flash and Supergirl, the Arrowverse featured a live-action version of the Suicide Squad not long before their first movie hit theaters. If that assessment is fair, it would mirror the company's strategy with comics and animation, where they have traditionally developed properties and familiarized the public with them before heading to theaters. Well-received animated movies starring Wonder Woman and the Suicide Squad both came out before those characters ever got films of their own in theaters.
Besides The CW's Melissa Benoist, the character of Supergirl has previously been played by Helen Slater in a feature film based on the character; and by Laura Vandervoort on Smallville.