I would like to see subsidies as a game concept.
industrial subsidies for those countries who want to develop a certain sector of the economy or at least prevent it from collapsing (maybe under free market parties unprofitable factories can shut down which will make pops more militant). laissez-faire parties would obviously grey out the subsidy slider, but liberal and socialist parties should be able to subsidise sectors of the economy, to a lesser and greater extent.
railroad/infra subsidies for those who want to provide government assistance in developing infrastructure but find that capitalists don't build where the player wants them to, or at all because they are tight bastards who sleep with their money in their mattresses. can open up strategies where subsidies can assist in the development of infrastructure in strategic areas.
colonial subsidies, which would provide an incentive for immigrant pops to move to a certain area. think of this as the government footing the bill for passage/land if an immigrant settles in a certain area. can help in settling places that are strategic but underutilised. each immigrant pop to an area would incur a cost to the treasury.
this could also open the door to taxation of industry by sector, which would assist state revenues. rather than factory profits coming to the states, a proportion of these would come to the state in line with tax/subsidy policy and the rest would go to the capitalists who, presumably, are the shareholder class.
it's a pipe dream, but i would like to see more then one resource available in a province, but a set limit on each provincial RGO size, so that if, say, one can grow sugar and fruit in a province, but it is a small island, only, say, 3 slots would be available, and so you could have 1 fruit and 2 sugar slots on the island. this would stop things like st helena having 100,000 people, all working on extensive tracts of farmland on polders reclaimed from the atlantic ocean.
perhaps as a province becomes more crowded, it's attribute could become more urban, with more urban developments unlocked (or always available but increasingly necessary) which would increase the life rating of that province. abstract things like administration, hospital and transport infrastructure, which perhaps would have one or two slots each to employ a pop (of a certain type perhaps, like a clerk) as well, if only to simulate the use of manpower in non-economic support and public roles. the efficiency of these facilities could be tied to the size of the one or two pops employed by them, as would the running costs of these facilities, which could be set at a level where only really prosperous and affluent societies could afford comprehensive public facilities.
population density could also be tied to life rating, which would provide an incentive to those who want population growth to build facilities to alleviate the effects of urban crowding. overcrowded or poorly developed and desolate provinces or with poor facilities would see emigration effects whereas well developed or relatively uncrowded provinces would see immigration effects. classic push and pull factors.
of course, warfare in a province should present a chance for infrastructure, factories or even public facilities being destroyed. the more prolonged the warfare, the greater the chance of expensive destruction and the attendant depopulation effects.