People know Superman's origin. It's not a mystery . People may know different post and pre-crisis versions depending on which version they grew up with, but it's not like anyone off the street would be baffled if you asked them where Superman came from. Superman the movie wasn't the first film to do his origin anyway and it wasn't the last . It's been done several times since i.e The cartoons in the 80's to an extent, Superboy, Lois And Clark, Superman the Animated Series , Smallville, SR to an extent, Not to mention reruns of the 50's series , serials etc and all kinds of media Superman is in. The public has had 70 years worth of the story being told and retold again and again . Flashes in the opening credits wouldn't be bad but really there isn't a need to go the STM route and do the whole thing all over again . Unless, as someone said , they do a radical change like the JJ Abrams version would have, there isn't a great need to shoe horn it in there imo.