Oh, I would
love to see Donna Troy treated as a "partner" of Diana. When Donna was first given an origin of her own (Man's World infant rescued from a fire by Diana, who took her to Paradise Island, where she was raised and essentially adopted by Hippolyta, making her Diana's "little sister"), everybody
talked as though Donna/Wonder Girl was Wonder Woman's partner the way the other four original Teen Titans (Robin, Kid Flash, Speedy, Aqualad) were the partners of their JLA mentors. But we hardly ever saw that
depicted in any way - for example, Wonder Girl almost never fought crime and evil alongside Wonder Woman, in
Wonder Woman comics, the way Robin did with Batman, Kid Flash did with the Flash, and so on. (We did get
The Wedding of Donna Troy, which I remember fondly, but it made use of relationships between Donna and Diana, and Donna and Hippolyta, that we almost never saw developed in the actual stories.)
Starting in 1986, though, with
Crisis on Infinite Earths, every new origin Donna Troy got only separated her further and further from Diana - either "geographically" (she was raised on New Cronus; started her career as Wonder Girl years before Diana came to Man's World and became Wonder Woman; and who knows when they even met for the first time?), emotionally (she was created by evil Amazons to be a weapon; she's not sure if she's human, has a soul, or is even really alive; and lately Diana treats her with suspicion, contempt, and disgust), or both.
As each reboot/retcon/rebranding approaches, I find myself hoping that they'll finally fix this, and bring back the loving, sisterly relationship Donna was once presumed to have with Diana, and make them partners. (And bring back her relationship as an adoptive daughter to Hippolyta, too.)
Instead I'm reading about Jason. By the end of this arc, he
already has a closer, sibling-style relationship with Diana (hugging each other, forgiving each other, mourning their lost parent - father, of course - and accepting each other as family) than Donna has had with Diana in years. Decades!
As far as Wonder Woman and her supporting cast goes, I'm way more interested in her relationships with Donna and Hippolyta than with Jason and Zeus.
As for Cassie, when she was introduced into The New 52, she had no known connection to Diana at all, and didn't even like to be called "Wonder Girl." At a very late date she was made Lennox's daughter and thus Diana's niece. But that was never developed, and was before "The Lies" and "The Truth." I don't even know if she exists in the Rebirth continuity (or, I should say, "continuity"), and if she does, what her origin is, and whether she has any link to Diana. (I don't even know if Lennox exists.)
I'd much rather see these characters (in which I've had some investment for quite a few years) developed, and these questions clarified, and see them actually made a part of Wonder Woman's family, before we spend a lot more panel time on Jason. But that's just me.