Each dev reveal is saying to me that we are replacing a sandbox with a curated forced narrative. This will likely put some restrictions on what modders can do.
Things like mandatory civ switching and era crises, as well as doing a soft restart are probably baked in pretty deep
Pretty sure the conditions to unlock a civ are not hardcoded but exposed in a database, else we (modders) would not be able to add new civs, and one of the few mentions of modding in the interviews was about adding new civs.