Well I have a whole list of ideas. I've kind of separated them into a hypothetical second season pass:
Pack 1: Iroquois and Navajo Pack- Nomadic Start game mode (similar to how Humankind is doing there beginning of the game by making a whole new era at the start of the game), World Wonders (Mt. Rushmore, Hoover Dam), New City-States: Mesa Verde (Scientific), Sheet'ka (Cultural), Luxembourg (Industrial), Dubai (Trade), Lhasa (Religious), Port Royal (Militaristic).
Pack 2: Haiti Pack- Colonization and Revolution game mode (Can establish cities on another continent as a "colony" by settling or conquering, which acts more independent but yields go straight to your capital instead of that city. Those cities have more of a likely chance to rebel and start a new kind of Cassus Belli "Revolutionary War".), Americas Map and Americas TSL Map as well as a Colonization Map and Colonization TSL Map.
Pack 3: Akhenaten and Berbers Pack- Akhenaten as a new leader for Egypt, along with a Schism and Reformation game mode (can "create" a new religion out of an existing one if you haven't found one), three new religious buildings: (Mandir (3 faith and 2 gold), Miào (Confucian Temple with provides 3 faith and +2 Loyalty, +2 culture if base game), Honden ( +3 faith and +1 Appeal to surrounding tiles), and reworked Great Prophets with each one having a separate charge for an ability in addition to founding a religion, New Religions: Jainism and Tengrism, Africa Map and Africa TSL Map.
Pack 4: Assyria Pack- Ethnicity and Cultural Identity game mode (Assigns each citizen in a city an ethnicity. Citizens that have a majority ethnicity in a city are more likely to be culturally dominant and if in a foreign civilization will cause more international tourists to travel to "home" civilization), Middle East Map and Middle East TSL Map
Pack 5: Austria and Italy Pack- Pandemic Game mode with GS rules (Comes with disease as a new natural disaster, Medical Facility district and Apothecary, Hospital, Health Clinic buildings, and Pandemic Emergency), Multiple new buildings for districts with most being mutually exclusive to others: Opera House, Caravanserai, Biological Research Lab, Chemical Research Lab, Physics Research Lab, International Terminal, Cargo Port, Naval Base, Public School, Cinema, Police Station, Circus etc., World Wonders (Notre Dame, British Museum), Turku replaces Bologna city-state, Kiev replaces Venice city-state.
Pack 6: Siam Pack- Ideology game mode (Ideologies can be a late game agenda depending on governments chosen), Kuala Lumpur replaces Ayutthaya city-state, Natural Wonders (Krakatoa, Mt. Fuji, Shangri-La?).