If they are indeed bringing over BNW features, I can see them extending ideologies right to the beginning of the game, with being a tree that spans the ages starting with despotism until we hit the ideologies of BNW.
So everyone starts out at despotism, branch out Monarchy/Oligarchy/Democracy/Feudalism , then into the 20th century ideologies. There would be different sub-branches to the trees to add flavour as well as separate a civic-like system or social policy tree layered on top.
But preference is have the governments work more like an earned experience skill tree, then have 'social policies' actually live up to their name and be more flexible and some social policies may have synergy combinations with the ideology tree choices, but, it's up to the players to mix and match.