Now that you say that I guess you are right, Justice League felt like it was 3 hours to me lol. So a whole other 2 hours of new content I guess I can see myself sitting through that. Still I like the idea of 4 chapters(or 2 viewings) and for some reason in my mind I pictured it coming along with a supplemental after show that talk about different points and keys to the movie.
What it is loses in cohesiveness from a straight up viewing. I think it could make up as event viewing. People would be tuning in every week and it would get the water cooler talk/ forum talk, Podcast and shows would be breaking it down and talking about it plus the all articles written about it over space of a couple weeks. And when the final show comes on hits landing they would be a sense of hype in community. There could be a benefit in parts as well.