“i don’t even think that costs and revenue needs to be adjusted that much. all the flow of time accounts for is availability of trains and stuff really. gameplay isn’t really affected by that, except for the cost due to ageing of trains.”
The problem with that is, you’ll just end up making the same amount of money in half the time, so it would ultimately be like a cheat that doubled all your income.
It wouldn’t need to be that complex… everything would just need to be scaled by that same factor, whether it was expenses or income, and it should ultimately balance out. In fact it should be more noticably balanced, because you would have less jittery annual accounts, as the overall income and outgoings would smooth out over time.