An option I like the idea of could be that we have a scaling production efficiency modifier tied to what portion of your production buildings that consume input goods are a particular type.
The equation I would propose tentatively would be: Cost Multiplier = .8 + .2(1 - Building Portion)2
If p is the building portion and c is the cost multiplier this would mean:
At p=0: c=100
At p=50: c=85
At p=75: c=81.25
At p=90: c=80.2
At p=100: c=80
So a player with 50% the same building would receive a 15% reduction in input costs for that building. If they increase that to 100% they would get a 20% reduction.
Some examples;
1. Let’s say you had a small empire with three permits, two metalurgy planets and one resource extraction planet. Each metalurgy planet has 20 SME on it and the resource extraction planet has 14 EXT on it. You would have a total of 40 production buildings that consume input goods as the EXT do not qualify, all 40 of which are metallurgy. That gives a building portion of exactly 1 so you would get the full benefit of 80%
2. Let’s say you had a medium rainbow empire with ten permits, 4 Metal, 4 Res, 1 Chem, 1 Fuel. In total this empire has, 80 SME, 16 CHP and 7 REF along with some Resource extraction buildings. This empire would get a cost reduction of very nearly 19% on it’s SME, 5.7% on it’s CHP and only 2.63% on it’s REF. This makes this empire significantly less efficient at it’s chemical and fuel refining jobs than a player dedicated to those buildings without very significantly harming their efficiency with their primary building, SME.
3. Let’s say you had a fairly large empire with 24 permits (values taken from a player’s real empire which is fairly well rainbowed); 3 Const, 3 Manu, 6 Elec, 4 Chem, 1 Metal, 1 Agri, 5 Res. In total, excluding buildings that don’t take input, this empire has; 9 PP2, 6 PP3, 15 PP4, 2 WEL, 22 SCA, 21 PPF, 16 ELP, 1 EDM, 5 DRS, 1 ECA, 69 (nice) SD, 33 CHP, 11 POL, 6 LAB, 5 PHF, 19 SME, 21 HYF, 48 INC. It goes without saying that most of these buildings would receive almost no cost reduction. The 69 SD’s would receive the highest cost reduction of only 8%.
This has the benefit that the player doesn’t have to assign any points or chose any specialisation, it is automatically calculated. The player is incentivised to specialize without being coerced into it. A rainbow empire will function almost identical if not exactly identical to current while incentivising players to source more of their goods outside their company. It incentivises intermediate products which are produced and exclusively consumed by the same cogc being traded, where other solutions given wouldn’t produce this outcome. It also allows anyone to participate in Resource extraction using EXT, RIG, COL as much as they want with no negative effect on the rest of their empire, allowing for more permits to stack extracting valuable resources on efficient planets.