User blog comment:Master Sima Yi/Assassinews 03-12-'14 — New Assassin's Creed in Victorian London leaked/@comment-5174994-20141206185227/@comment-13471981-20141206193159

Synching viewpoints is not enough (it only clears up the map) as it does not automatically reveal the locations of collectibles. I think the chests and cockades show up on your mini-map once you're in their vicinity (it's a similar mechanic as in Liberation). From then on they'll be visible on your large map as well.

No idea to the other two questions. I thought Dead Kings was already available, actually xD