I guarantee SNC is not “design(ing) a successor to the E-4B”, unless it’s going to be a version of their Dreamchaser, and only carry a couple of people. SNC has no such capability to design and produce a jumbo jet. They will still have to choose either Boeing or Airbus, with SNC perhaps designing the internal systems.
Yep, looks like it is going to be retrofits of used 747’s:
https://breakingdefense.com/2024/04/air-force-awards-snc-13b-contract-for-new-doomsday-plane/
https://www.sncorp.com/capabilities/aircraft-integration-modification/