I would like to see some logic behind the map generator for rocks and minerals (especially coal).
Simply put, coal is most commonly found on earth near shale, sandstone and limestone, thus I believe the Map Generator should attempt to place coal adjacent to these rocks.
I don't mean every single node of those rock deposits come with a node of coal attached, but in the event coal is generated it is accompanied by an appropriate, realistic rock deposit near it.
Coal is important and there should be a method or logic to finding it outside of tunneling and grid mining.