Obviously, with only 67 industries, what FIRS really needs is MOAR INDUSTRIES. So here goes with my 2 cents.
Please note I'm only talking about the FIRS economy here, so temperate environment.
First, the Power Plant: I don't like it. Coal is already over-taxed as it is, with five separate secondaries calling for it, and the power plant is a black hole, not adding anything itself. But it's a great cash cow.
Also, is it possible for an industry to be forced to close by making it obsolete? That would add more flavor and potentially more depth to the early-start games, while keeping the map from getting cluttered with anachronistic businesses (smithy forge, I'm looking at you).
I saw in the code that default houses require the Goods cargo to be functional or they break; I'm about to advocate breaking goods down into separate cargos, so I don't know if that would work at all. Anyway, here's the suggestions.
The goods chains:
Each of the goods-producing industries (Textile Mill, Paper Mill, Plastics Plant, Glass Works, and Metal Workshop) produce (in addition to any mnufacturing supplies) their on unique cargo: textiles, paper, plastic, glasswares, and metalwares, respectively. Some of these (paper, glasswares, and metalwares) can be sent directly to terminal industries, while others (plastic, textiles) have another step or two to go. I'm adding the Glassworks to this, obviously, so whether it keeps Building Materials or not as an output would be up for discussion.
Textiles, for example, gets sent to a Clothes Factory (with Manufacturing Supplies) to make clothing.
This permits more depth in the supply chains. For example, an Automobile Plant can require metalwares (representing parts), glasswares (representing windows and lights), and textiles (for the upholstery), and make cars that get delivered to a Car Lot terminal industry.
So here goes with the full list. Please bear in mind I'm only writing down changes, so even though I'm not writing it down, the Paper Mill still takes in wood and chemicals and still outputs ManSup. I'm referring to them by tiers, because I don't know what comes after "quaternary".
Arable Farm: add Vegetables to production
Cereal farm: produces crapton of grain
Silver mine: produces Argentite
Cannery: Fruit, Vegetables, ManSup -> Food
Grain Mill: grain -> flour
Sugar refinery: sugar beet -> sugar
Textile Mill: chemicals instead of ManSup -> textiles
Metal Workshop -> metalwares
Glassworks -> glasswares
Paper Mill -> paper
Plastics Plant -> plastic
Oil Refinery -> petroleum products (just a name change to acknowledge products other than gasoline)
Silver Smelter: argentite, chemicals -> silver
Cannery: vegetables, fruit, ManSup -> food
Bakery: flour, sugar, ManSup -> food
Clothes Factory: textiles, ManSup -> clothing
Furniture Factory-> Furniture
Silversmith: silver, ManSup -> jewellery
Mint: silver, metalwares -> valuables
Microchip Factory: sand, plastic, chemicals, silver -> microchips
Port: metalwares, glasswares, clothing -> coffee, rubber (because another source of EngSup is boring)
Electronics Plant: microchips, plastic, glasswares, silver -> electronics
Automobile Plant: metalwares, rubber, glasswares, textiles -> automobiles
Appliance Factory: electronics, metalwares, plastic -> appliances
Equipment Factory: electronics, metalwares, glasswares, plastic, rubber -> Industrial Equipment (can be fed to primaries already going Gung-Ho to further increase production to 6x. No other effect. This is intentionally a really hard chain to set up.)
***Terminal Industries - consume without producing.
Newspaper office: paper
Fuel depot: petroleum products (rural version of gas station)
Car lot: automobiles
General Store (obsolete in early 1900s): food, alcohol, clothes, glasswares, metalwares, furniture, building materials.
(Builder's Yards, Grocery Stores, Luxury Goods Stores, and Department Stores show up once the General Store is obsolete.)
Grocery Store: food, alcohol, fruit, vegetables, coffee
Luxury Goods Store: jewellery, glasswares, clothing
Office Building: paper, furniture, electronics (maybe generates mail? Represents the aggregate demand of offices in the city. Should be restricted to large cities only, say over 3,000 or so.)
Bank: valuables (maybe generates valuables like Pikka's)
Department Store: electronics, clothing, glasswares, metalwares, furniture, appliances, jewellery (should be rare, probably city-size restricted like the office building.)
Edit: forgot to add that I'd be happy to help code. Took a glance at the source and it didn't seem too scary, but there's too many moving parts for me to be completely confident I wouldn't make it all snarf.