I think it would be much better if tunnels could be stabilized so every tunnelpart has an integrity which is most of the time stable but could get worse because of influences from outside. That mens in some parts of tunnels there where a need for support logs or boards.
And the urgently thing which have to get fixed is the blocking area around tunnel so at least we should be able to fill up old tunnel systems.
Otherwise it would be helpful if stone could be flattened too. It is shit that stone only can digged and after that it is a tunnel even if it is upside on earth ground.
sorry for my bad english hope everyone knows what i mean XD