To my knowledge that capability has been around for a long time, they just changed the UI for it. Beneath that, nothing has changed about the fundamental problem with Scrivener supporting this: it has no architecture for opening the same project more than once, and given how iOS works in a somewhat “stateless” fashion, it would be very difficult to know if a project is already open. The latter, if it could be done reliably, is how we could implement this safely: if the project is open in another instance, then you simply couldn’t open it again, it would stop you (that’s how the desktop version works). Thus without that, we’d have to make that possible, and that would require a probably ground-up rewrite of an awful lot of stuff.
As for working with more than one thing at a time within a single project though, that has always been a feature.