the biggest problem at the later stages in the game, is that you cant keep up yr Coal production, without trying to buy it. because you use a sick amount of it per 12h. you can easy get to stage where you need 30k + coal per 12h. at lvl 40.
and at lvl 45 its like 50k+ Coal for 12h. you just cant keep up with it, regardless of how many coking plants and so you have.
because of it, its would be really nice to make a High lvl Coking plant like lvl 36 or so for example, that use Hardwood Logs to produce Coal. it can be the same coal. but production would be for example 2 coal out of 1 hardwood log. because hardwood cutters need a little longer to cut as pinewood cutters. It would be a balanced, but real good improvement in the game.
its easy to implement for Blue Byte team. and would make this game better.
greetz