New building boosting your City-State influence could be a good one. There was a Compilation topic for new additions (Buildings, Techs, Units, Terrain etc.) a long time ago. There was some good suggestions. I especially liked likes of Zoo, National Park, Oceanographic Institute and Ski Lodge.
So the great date of announcement? I'm guessing now it will be either Thursday 14th or 21st of this month.
What about airports? It seems like a large area of civilization with no representation in civ 5. then you can make it a natl. wonder and have an international airport that has diplomatic abilities.
I think the announcement will come a week before PAX east. That way they can build buzz about the conference.