Playing Tropico I always had Idea that your Republic is always too communist even if it's planned as capitalist. Because everything belongs to state. For that, I suggest to get best practices from previous tropico games and simcity series (with adaptation).
First mechanic will go from Tropico 2. Yes-yes, this about pirate era. But it had very cool thing, you just mark a lot, and free resident build there own house, and develop it regarding it's wealth. That could be income line in your budget, because for example you play X$ for administrative things for putting lot for sale. And after that someone buy it (gives you Y$) and pays taxes yearly (0.02Y$). It's about small individual residental lot. They could be one type of various, regarding development resourses. the most basic - 1x2 or 2x2. This individual houses can have parking lot. Additional idea - big lot for sale 2x3 or 3x3, where Rich Landlord can build a "income house" with appartments for rent. All other is same as other residential house, with sale of lot, and tax paying system.
Second mechanic is going from Tropico 3 (as I remember). In some missions there were option to build some private objects. For example I remember ability to build private cigar factory and option to have private oil rig. That could be useful for our island too. Resources for this factories could count as "inner export" or something like that. And they will create workplaces and pay taxes without state investments. Or with partial, for example 49% of Republic and 51% of Investor, local or foreign.
Third mechanic is completely new, inspired by simcity series mainly. You create commercial and industrial lots. 2x3 and 3x3, for low and high dencity. And investors buy it and create own enterprises, which could serve various needs of citizens. It could be Entertainement (for example video or book stores,, shops of import goods, private zoo and many many other types), Health (private clinics), Safety (private security agencies), food (restraunts and cafes, shops of import food) or even freedom (private newspapers or other media), and also hotels or even wealth (for example, visiting investment company will increase give Entertainement and give some chance to move visitor on higher wealth category. Or lower (but that could be disabled by special law, like "law about risk managment or low about qualified investors). Same for industry, it could be small or small and big, relating to development recourses. For example local buisnesses which create steel utensils, wooden toys, metal motorcycles or bicycles, and many stuff like that. With negative effect to ecology or without it.
Final mechanic is mechanic of managers. On every workplace - everyone is equal, full communism. I suggest to fix it with ability to open vacancy of manager, which will increase efficiency of object. Chief of police station, director of factory, manager of the logistics office and other. Manager requires +1 one more stages of education, unlike workers. For example director of factory will need a college degree, when director of farm only school grade.
And all this mechanics will open a space for dictatorship things too, for example any object can be bought back with just bonus of market price (with very small fall of efficiency and no hate from owner), with just market price (with average fall of efficiency and low negative from owner), with formal price (with average fall of efficiency and moderate negative from owner) or just NATIONALISED (with big fall of efficiency and big hate from owner). For example, you started to build capitalst country in world war era, but hypotetical communist turn around forces you to kill capitalist economics and nationalise all. In modern days "communist period" ends and you give back this nationalised (or bought for formal price) property to owner for free, or re-sale it to new owner in market. Same, investment climat is your new parameter, which shows how investors see your island for buisness. Good - land buy go faster, foreigh investors can come. Bad - all process are slow and foreign investors are not very interested in your republic.

That my idea. Waiting for feedback and hope to see addon like that. In fact, that should simplify game, because Republic's economic will not be state-only, and you will be able to rely on private capital and get some profit with minimal start costs.