This all looks great! Envoys, controlling their armies with gold (suzerain), unique bonuses, more than 2 bonus tiers, color-coded borders (love this -- types will be easier to spot)... so much good stuff.
I learned a new word today too; woot! ("Soo-zer-en")
Also, each CS looks like they can hold a lot of quests; the ones pictured have 6 each.
I wonder if influence can be gained in other ways, such as intimidating the CS with a powerful army nearby. It would be fun to still have tributes which can be demanded and such, and a much better pledge-to-protect system than there was in Civ5. Actually... scratch that. The article says that things have been streamlined, so it's probably mainly focused on envoys.
Also, I'm curious if those unique suzerain bonuses for each CS are truly unique to every CS in the game, or if they're assigned from small pools of bonuses that each type can have. As in, Jerusalem rolled unique bonus #2 out of the 3 different suzerain bonuses that religious CS can have. Though, cinnamon and cloves are pretty accurate for Zanzibar, so perhaps they really are unique.
Also, it looks like they're continuing to roll with gold's yield value equaling about half of the other ones.
EDIT:
Those slingers look pretty cool too; first time I've seen them.
EDIT 2:
On top of the interface, it looks like stone and wheat are quantified, just like strategics! I wonder what new systems have been created. I'm not sure what that other one is, between the wheat and horse icons. Could it be a luxury (tea)? That bar would fill up pretty fast; though, there is a ton of space up there.