Showrunner Greg Berlanti's shared DC universe on The CW blew up recently with the two-night crossover event between The Flash and Arrow (referred to on Twitter with the rather dubious hashtag #Flarrow), which provided a viewership boost for both shows and scored record high ratings for Arrow. The success of the crossover experiment has only intensified speculation that Berlanti might set his upcoming CBS show Supergirl in the same shared universe.
That kind of planning is some way off, however, as right now Supergirl still needs a super actress to play its title role. A number of twenty-something actresses are currently being tested, but one of first names to be revealed was Claire Holt, star of supernatural series The Originals and The Vampire Diaries, who recently exited the former show. While this might have freed up her time enough to play the lead in Supergirl, a new report indicates bad news for Holt fans hoping to see her super-suit up.
Obviously Holt was just one of several actresses up for the part of Kara Zor-El AKA Kara Danvers, and THR sources claim that she is not expected to get the part. Whether this is due to the producers being interested in someone else or due to a clash of schedules is unclear, but Holt does have other work on her plate; she's set to star in upcoming NBC drama Aquarius, and the article also indicates that she could return to The Originals in the future. Signing up for a lead role in Supergirl would be a major commitment, so it's possible that CBS is just looking for someone with a bit more free time.
There isn't exactly a shortage of young, blonde actresses on TV right now so speculation as to which one is likely to end up playing Kara is pretty much a stab in the dark. It will most likely be someone that hasn't really made a name for herself yet; prior to taking the lead role in The Flash, Grant Gustin was best known for guest-starring in a few episodes of Glee and playing Oliver Queen on Arrow was Stephen Amell's first major role, so another newcomer is likely. With a show that's almost certain to be effects-heavy, the chances of CBS spending a fortune to get a well-known actress in the lead are slim.
Supergirl will feature an origin story that's slightly altered from the comic books, with Kara already an adult who has been disguising her powers for years. At the age of 24 she decides to finally embrace her abilities and become a hero, while also harboring a crush on her colleague, James Olsen.
Supergirl is expected to air on CBS in 2015.