Proposal: Talia, not Selina, should be Batman's primary love interest in a rebooted DC cinematic universe.
This will no doubt be controversial, and probably surprising coming from me, a vocal BatCat partisan. But I've thought it over, and I really think this is the way to go.
Batman has had two main love interests that overshadow any others- Selina Kyle/Catwoman, and Talia Al Ghul. But while BatCat has been centred in recent decades across different media, Talia has tended to get overshadowed-and outright bashed (ie the incredibly stupid decision to retcon her into a r*pist, though IIRC that's been re-retconned now). Some of her depictions are outright racist. And her one big live action film appearance, in The Dark Knight Rises, gave her dubiously plausible motives, very limited screen time as Talia, and whitewashed the character.
Which brings me to the second point- we already have a recent/possibly ongoing BatCat on film, in the Reeves films. Assuming that they remain in their own continuity, and the DC Cinematic Universe under Gunn gets a new Batman, that represents an opportunity to explore different aspects of the characters. Further to this, having Talia be the main love interest would be a way to differentiate DCCU Bruce from Reeves/Pattinson Bruce.
Third Point: Talia opens up a lot of other story options for an ongoing, shared universe. She has ties to one of Bruce's main villains (Ras) as well as a number of other secondary villains involved with the League (Cain, Shiva, Deathstroke, etc). She also in comics worked with/for Luthor for a while. And she has ties or could easily be tied to the origins of at least three notable Bat Family members: Damian, Red Hood, and Cassandra (who's parents are both affiliated with the League).
In other words, its simple narrative economy. Talia goes hand in hand with a whole established cast, allowing a DCCU Batman to have a more streamlined story and character introductions- which is vital if we want to see a proper Bat Family developed on-screen. This is similar to the approach in Gunn's Guardians of the Galaxy, in which a large cast were quickly brought together by shared connections to the main villain (Gamora, Drax, Nebula) and/or pursuit of the same treasure.
Of course I know that the films are probably more likely to push Bruce/Diana, because in a multi-franchise shared universe the instinct is likely going to be to crossover and pair two of their big leads. I get that. But Diana doesn't have the same history with Bruce that Talia does, nor in my view does that pairing open up as many story opportunities. It also, frankly risks Diana being overshadowed by Batman, as he is probably a bigger and more popular character (even though this shouldn't be the case).
I also know that the old Talia the r*pist plot line might make the character unusable, even though that was basically just character assassination by one author in a decades-long franchise being an idiot, the films are a different continuity from the comics, and IIRC its long since been retconned. And it would likely get the MRAs up in arms screaming about a "double standard" and that men are the real victims of sexism. But, you know, fuck them.
Personally, I think the biggest advantage lies in the other characters you can tie Talia's story into. Talia as Bruce's love interest comes with a half-dozen potential rogues and half a Bat Family built in. I would therefore go a step further and say that DCCU Batman's primary antagonists should be the League of Assassins (if he has his own main enemy outside of the big crossovers like Lex and Darkseid).