To begin, if Walt’s son isn’t involved, then there’s a solid chance that this sequel might not revisit Walt’s family at all.
The fact that RJ Mitte is not involved could tell us a few things about the Breaking Bad movie, which is allegedly in production in Albuquerque under the name Greenbriar.
Granted, it’s possible Skyler and Holly are still living together and Flynn is off at college or something, but this could be confirmation they just aren’t involved.