The difficult part isn't designing a means of switching from one battery pack to another, it's convincing regulators that took decades to be convinced by things like two engines being enough redundancy that a mid-flight power source change is a good idea
Bureaucracy is not the problem being posed here. It was a question of technical possibility.
When I said it's trivial, I meant trivial. You can simply just discharge one pack preferentially over another. It's something that would be inherent to the power management circuit.
Whatever you're imagining, this is not that. There is no giant lever to changeover the packs. The circuit is never broken and power is never interrupted. It really, truly is as simple as drawing power from one battery and not the other.
Given the ridiculous power requirements involved, 'simple' is perhaps a bit generous. But the complexity is in physically handling that amount of current, not in switching it. Again, these are solved problems with standard solutions. This is stuff we've been doing industrially for years.
