Newgrf sets could change and limit this. Perhaps add some conditions to the growth.
Here's a little suggestion that adds a twist to what newgrf industries can do:
The basic idea is that, once certain conditions are met, the player can manually expand the industry's production. However, if the conditions for the current production level are not satisfied any more, the industry reverts to its previous size (it cannot maintain it's current size).
Here's an example (assuming the default factory):
- No condition, maximum production 256.
- Have at least 1 vehicle with orders to pick up goods at the nearby station
Maximum production 512
- Have at least 5 vehicles with orders to pick up goods at the nearby station
deliver at least two cargo types to the factory
Maximum production 1024
- Have at least 25 vehicles with orders to pick up goods at the nearby station
deliver at least three cargo types, of which at least 512 each, to the factory during a month
Maximum production 2048
Requirements for an expansion could include any from:
- Flat cost
- N Vehicles with orders to pick up produced cargo at nearby stations
- N nearby stations receiving cargo from the industry
- N types of cargo delivered a week/month/year
- N types of cargo picked up a week/month/year
- N cargo delivered (maybe even per type)
- N industries need to be near the local authority
- N% of the industries (of type X) near the local authority need to be at level Y
- Nearby town minimum size
- Nearby town maximum size
- Specific local town rating or higher
- N% transport rating of cargo or higher
- N cargo or less waiting at station
- Other industry in chain, where cargo is received from, must be at a certain level
- Other industry in chain, where cargo is sent to, must be at a certain level
- Specific date in game or later
- Minimum industry production/month increase
- Maximum industry production/month increase
- Town rating increases
- Town rating decreases (imagine living near a nicely pollution coal power plant, would you like it if it expanded?)
- N New industries in the production chain appear between X and Y tiles distance away.
- New cargoes are accepted/produced
- Industries of type X in range Y close down/have their size (upgrade level) limited.
- Likelihood of nearby towns/industries offering subsidies to you increases/decreases
- Next industry in chain is allowed to expand
Here's another twist: if you invest too much in N% of the industries on the map (setting, perhaps?), you get fined (market manipulation). The first time you get this fine, it's like a slap on the wrist... but it grows (exponentially? parabolic?) as you get it more and more, until it costs you billions. This could be expanded to say "if you invest in X% more industries on the map then your competitors, you get fined"
The whole point of this idea is to create a money sink and add some more difficulty to the game. However, this could be optional as an industry grf needs to deal with this. Now, the default industry set could just ignore this and be fine, but if an industry set does support this, it's bound to increase the involvement in routes already up and running, especially when breakdowns are set to none. This also helps against one player running off and leaving all the other players behind, staring at his billions, while they only got millions.
Industries could also ask players who have "invested" in their upgrades for a friendly loan/further investment. If this loan/investment is not met, various things could happen (reduction in industry size, a disaster (accident due to the industry not being able to invest in safety measures), nearby town rating dropping, next expansion becoming more expensive, etc.). Of course such requests for loans/investments could increase in size depending on various things, for example on an incoming disaster (maintenance urgently needed) or meeting the requirements of the local authorities (facing shutdown or production stop if rules are not met), industry expansion (not enough funds for that). Of course there would be some sense of randomness to all of this... however, odds of this happening to a particular industry could increase as its size increases, and the loan/investment it requests could become larger with its production size. For additional fun, this could be manually be triggered... but if discovered by the local authorities, it could net the player a huge fine (anti-competitive behaviour, ironically ).
If you see a potential hole in all of this, please think in solutions and not in problems.