Didn't they claim to already have a baseline of Persistence quite a few months ago ? 
Character state persistence went online a few months ago, world state persistence will be coming with 3.0.
3.1. is the new Jesus patch ?
No, that's still 3.0. 3.1 is supposed to add some more gameplay options, but 3.0 is when the persistent world will go live. At that point, Star Citizen finally becomes an actual MMO, even if the scope is initially quite limited.
Is that the Vertical Slice they were barely days from finishing last year but later said they aborted because it was expanding efforts on something that ultimately was a demo separated from the main branch ? What ?
Unlikely. The original vertical slice was, as you wrote, a different branch. The new VS should be a polished section from the actual main branch.
CiG guys goes "YES! OF COURSE!" then lays out mechanics that do none of that. Based on what he is saying it will just be a cargo slider and your ship burns more fuel the higher the cargo slider. As for achieving orbit every ship will be able to (meaning that mechanic doesn't exist) and it's explained away as "No ship will have a cargo hold large enough that it can't achieve orbit!"
Mass doesn't prevent you from orbiting something, unless it's higher than the mass of the object you're trying to orbit. Then said object will instead orbit you. So, unless you can load black holes in your cargo hold, I don't see what this is supposed to be about. There are no orbital mechanics in the game right now though, and I'm pretty sure they won't be in the public alpha for quite some time.
And the cargo management has been shown very recently. You can load/ unload bulk cargo with a slider, and the system will distribute the containers automatically. And yes, cargo has volume and mass, and mass distribution is supposedly taken into account for the physical simulation. If you manually grab a container or something and shove it in your cargo hold, it gets secured to the floor where you put it.
Full universe simulation and 20 million AI agents just feels like them throwing out nonsense with no context.
It's just agent-based economic modelling using AI, with the number of agents being around ten times the number of registered players. It's purpose is to limit the player impact on the economy. It's not nearly as amazing or outlandish as it sounds.