1) My major ask would be to increase the extent of private sector actions, in particular:
a) private sector infrastructure (factories, railroads, etc)
Private sector capitalization should be a major feature in several countries - UK, USA most especially.
State-sponsored factories, railroads, etc occurred in Europe because the private sector wasn't rich enough to build the infrastructure the governments wanted.
So make capitalists richer and have them invest surplus capital in building factories and railroads and only a proportion in state bonds.
Of course the returns from such factories/railroads should flow back to the capitalists who funded them, not the government of that country - unless you nationalise them - which would be almost certain to give you a war with the capitalist's nation (probably UK, possibly France).
Protecting you capitalists assets/income in minor nations would then become part of your diplomatic plan.
Theoretically the excess funds of rich Capitalists in UK should be funding industrial development in USA and South America (as actually occurred), provided the government was "stable" (communists need not apply!).
b) self-initiated POP advancement
Some of various POPs should develop into next class (Labourers/Farmers -> Craftsmen -> Clerks -> Capitalists), if they have excess funds (ie are getting most/all of luxury needs) and there is high education spending. Shifting to Craftsmen should accumulate as potential shift (ie # of potential Craftsmen available) if there is still work available as Labourer/Farmer, but not as Craftsmen (ie POPs don't advance themselves into unemployment!).
I would even encourage removing (or at least making much more expensive) the ability to manually change POP type.
This would mean that governments that had high poor taxes and low education funding would find it difficult to industrialise. Conversely countries with modest taxes and strong education systems would have the ability to industrialise.
2) I would like to see a more advanced loan system.
For instance, Russian diplomacy was strongly influenced by the need to raise loans - the French could (and did) provide access to loan capital, whereas Germany could hardly finance its own expansion, much less Russian.
At the moment, loans are raised and interest and capital repaid, but this money is created from nothing and disappears similarly.
Instead have (notional) capital markets in each country (funded by capitalists?), which can be accessed for loans. So Russia can try to borrow domestically, but available funds are small, or borrow internationally (but can be blocked by unfriendly governments).
3) Model mechanisation of RGOs
During this period much agriculture and other RGO-type operation were increasingly mechanised (esp in US under pressure of relatively high real wages - see below). This greatly increased productivity of these operations, without the need for increased numbers working at the farm/mine. IMO the process of putting railroads to improve productivity does not adequately reflect these developments.
4) More sophisticated immigration system
Make the immigration system more realistic, so that it will reproduce the US immigration flood only if circumstances correspond to history (ie not just hard-coded).
In particular, track relative real wages, driven by supply and demand for labour. Hence USA would tend to have (as historically) high real wages, due to demand for labour to exploit natural resources and later to man factories, etc. The gold rush phenomenon could be reflected in the real wage rating (rather than artificially in the life rating).
Relative wages, social/political conditions and physical conditions would drive emigration and immigration. Governments could (and historically did) shift the balance in their favour by offering assisted passage and similar inducements.
Real wages should interact with profitability of factories (and RGO) - so high real wages would reduce profitability. [NB labour costs are then a factor input, and not just physical inputs].
5) Regionalise markets
Markets should be regionalised, not just world market, especially for bulky goods.
Transport costs should influence relative prices - so that coffee is cheaper in Brazil than in Tibet! Also transport costs are volume/weight related, so expensive but small items such as machine parts would be little affected, but fruit would have major differences.
Local cost of input into a factory should be determined by delivered price = market price plus transport costs. So factories will be located close to their raw materials, rather than in (say) Alaska, because there are a bunch of would be gold miner POPs there!
Transport cost should be based on travel time - overland should be high cost until railroads are present, sea transport should be relatively cheap (esp after steamships become reliable post 1850). You could hardcode existing exceptions for countries with significant canal systems in 1836 (eg UK, US Great Lakes/NY for Erie Canal effect, etc).
Uncivs would only be able to trade in their regional market(s), unless they signed a commercial treaty with a civ (giving them access to that civs markets).
