On a related note, is there any indication that there will be vassal-type relationships between Civs?
I haven't seen any indication they're back but may have missed something.
Cheers
None. It seems that city-states occupy that part of the game now, as enough envoys is supposed to effectively make a city-state your vassal.
To be more specific, the highest status you can reach with a city-state is "suzerain", which under all definitions I can find effectively makes you the master of a vassal.
It's not really useful considering the only point of puppets was to not get hit by the unhapiness of a freshly acquired city and the culture penality.
With both of these gone puppets have no purpose.
Since there is no global happiness or culture penalty per city, the reasons they were in CiV are gone (except from the warmonger penalty). So I'm guessing they're not in.
i'd like to see each civ leader in sock puppet form