The Arrowverse producers love their crossovers, there is absolutely no way we won't get numerous Superman & Lois Lane and Supergirl crossovers.
I'm wondering if there's some prominent Superman/girl-centric event in DC Comics that could be the basis for a future crossover, centering on the Supercousins and bringing in Flash, Batwoman, White Canary, etc. in supporting roles. There was that New Krypton thing a few years ago, but that's kind of similar to what Supergirl did in its first couple of seasons.