I think a ball court as coloseum replacement with +faith is likely. Ritual sacrifice was a big part of the game IIRC.
I would also like to see a temple/obseratory type building. I think a temple with science benefit would be better, but observatories with faith would work too.
I am really hoping they get 2 UBs though to differentiate them from the more warlike Aztecs
Do you think any other civ will get a UI like the Dutch, or is 1 in 9 enough?
And what about two unique units? We know the Huns and Carthage have two, and many suspect cataphracts will join the dromon to give Byzantine two as well.
I think the Celts will have two UUs and the rest one of each, as any ideas I can think of a unique building seem boring or better unique buildings exist (i.e In what way can the Dun be better than the Walls of Babylon, unless they give it something unrealistic like a faith bonus)
Let's go through the list for possible UIs.
Carthage - No
Huns - No
Austrians - Probably Not
Byzantines - Probably Not
Maya - Maybe, but I can't think of any
Celts - Possibly
Ethiopia - Possibly
Mystery Civ - Possibly
Atlatl might have jungle bonuses, fwiw.
Allow it to reach its full range while in jungle? (i.e., selective blind fire for jungle).
For the Maya you could have the UI: Cenote and the Step Pyramid could work as a UI. I like to joke with family whenever I am in Guatemala that every other hill is actually a ruin. But really there are so many ruins and pyramids all across the Maya world that it could be a UI. Its not what people picture when they think of the Maya, but the Jungles had shrunk a great deal with the extreme urbanization our ancestors achieved.
That could work, or something I was thinking of was maybe a poison effect where units hit by an atlatl suffer small damage per turn until they return to their own territory/cities? Might be too powerful, maybe until they heal next to a fresh water tile or unit with medic?
Or maybe even those units hit by an atlatl suffer a strength reduction penalty like the maori ability which lasts for a set number of turns.
As I've said before, I doubt they'll have a Cenote as a UI. AFAIK, the Mayans didn't actually dig cenotes, they're a pre-existing terrain feature of the Yucatan landscape. Step Pyramids, on the other hand, could be a UI that generates faith (similar to Polynesia's UI that generates culture & gives a combat bonus to nearby units).