Yes, it does seem like Lois will be co-lead, if not the actual lead. Gunn has repeatedly asserted that it is "Superman and Lois" movie, which honestly disappoints me. We haven't had a good Superman movie in 45 years and now he has to play second fiddle?
I think the Krypto thing was a joke. Someone suggested it online and Gunn went along with it.Krypto is in the film so presumably Supergirl is on Earth too.
This seems like a bad idea. Superman is one of their big guns, he should be the one getting the big movies. Gunn would be insane if he is pinning his hopes on Supergirl of all characters to deliver the big movie.BTW, it's not looking like you will get that "something bigger with Superman" in SL. However, per the descriptions of Supergirl's film it will be a universe spanning epic so you might get it there.