I don't think they have plans to go that far,Wyn, at least at present!....But wouldn't it be wonderful if they did!
You do, however, raise one of the seemingly insuperable problems that face any railway from quarry to port. This relates to the plans (on another thread) to increase export, by sea. I may be totally wrong but it does seem that, if it goes ahead, it will be road transport from quarry to port, which seems to partially defeat the idea as seen by many people. An increase in the heavy road traffic from the quarry will not be welcomed by alot of people. By the same token, any re-instatement of either rail system will not be welcomed by alot of other people.
Rocks and hard places!