That's what I was hoping to see from the game demo during the keynote, but they didn't allude to it. That's the next key element we're going to need.

not yet. right now ARKit feature points are not 'persistent'. Meaning, they are only really used to help track 3d space frame over frame (with the internal gyro). Getting a 3d map that can be shared with multiple people is another layer of complexity not yet integrated into ARKit