1. Oh, I didn't know he was going to have a larger role in Supergirl
2. Why would Brainiac do all this stuff to test only Kara and not Kal-El? Because it's her movie?
Why would he think she's more fascinating than his male cousin? Why wont he give him a lot of challenges and obstacles too?
Is Superman supposed to be only a pawn on the chess board, and Kara is the real big thing?
3. Really cool that she's teaming up with with evil mastermind Lex to take on the otherwordly threat.
Will we get to se Brainiac taking over his body, as in the comics?
Well in answer to 2 : The film is truly Supergirl's film ,with Superman being a supporting character who shows up in the middle, and helps her in the finale.
As far as testing goes, It's a fixation with Kara that he doesn't have with Kal El, in this version at least.
He already has her doppleganger in Powergirl , whom he's shaped, molded, and manipulated to obey him and to serve his needs from Powergirls childhood up to the present. However, Since Supergirl has become a public figure she has become his new obsession.
The way I would picture it happening is that , in a sense , he can't figure Kara out and in his mind, he can't classify or quantify her. Unlike Powergirl, who he feels he knows her ever thought, feeling, and whom he thinks he can predict how she would respond to stimuli, with Kara, he sees contradictions that he can't reconcile .
She's young, beautiful, powerful, good, loyal, kind, fierce when she needs to be, yet still naive. In a way, he thinks so little of other creatures, that he can't believe that something or someone can be all of those things at once. It's that basic lack of humanity and understanding of humanity that he almost considers a glitch.
So he's obsessed with her.
In alot of ways, there isn't a grand scheme in terms of destroying earth or killing Supergirl or Superman for that matter. It's a simple, and single minded focus, but its played out on an epic scale and using Superman and earthlings as pawns and collateral damage.
It's like he would be willing to risk the whole human species ,and whatever he could take from them, just to resolve the anomaly
he considers Kara Danvers to be.
On Powergirl's end, she begins to feel a twisted sense of jealousy towards Supergirl, since Brainiac is the only friend, mentor figure she's known, and in a sense , she fears Brainiac will replace her with Kara, even though they are basically like sisters and have a shared past that she is unaware of.
So I picture the film being very much a eternal triangle with these three characters( Supergirl, Brainiac, and Powergirl) all locked in this conflict , with Lex trying to see all the angles and use them to his advantage.
As far as Superman goes, I imagine that Brainac somehow tricks, and captures Superman off screen and keeps him captive in one of the many tanks he collects creatures in, so in a sense he's like Han Solo in the carbonite in ESB.
So its the
Superman Returns idea of him just vanishing out of the blue, except this time , he's not doing it purposefully. Lois begins to investigate and she's caught to.
Superman is a pawn in that sense. Braniac goal is to get him off the chessboard, otherwise he could stop Brainiac in his tracks. It takes him off the field and basically forces Kara to have to step into the vacuum because of the high stakes.
Superman would be off screen for at least the first act of the film and he we would see Superman and Lois in captivity in act two basically.
These events would be revealed and discovered by Kara as the film goes along , but the film would begin with these global tensions beginning to happen and people basically scrambling.
The crisis, basically forces Kara and Lucy to leave their High School and go to Metropolis to find Clark and Lois.
As far as Brainiac taking over Lex's body goes, I never thought of that, but I could see him trying to control Lex in the third act.
I could see him , as played by Jeremy Irons, being mostly in the humanoid form that he's been in Smallville and Krypton for most of the film , but I could also see taking some of his consciousness an attempting to download it into Lex.