I've not seen everything and unsure if some is speculation.
Are they saying the S&B film is it's own thing OR that the S&B film is a de facto MoS2?
If its going to be it's own thing, great. I've thought a Worlds Finest movie was necessary before a JLA anyway.
If it's de facto MoS2 I feel it jips Superman of the necessary solo world building. Especially after the events of the film in Metropolis and Smallville.