A railroad network is a game changer feature delivering a new fresh gameplay experience

"Armored trains" yes obsolete but not for guerilla fighters where an anti aircraft platform can be easily towed to a train locomotive

Military operators can infiltrate passenger trains to move across the map without drawing enemy's attention.

The trains can transport valuable logistics, weapons, ammunitions, vehicles from a port or an airfield to different part of the island

You can ambush/raid these trains and get your hand over their freight

Destroying one of them will serve for many scenarios like :

-Prevent smuggling/arm dealing/exporting illegal products (weed) out the island
-Cutting off enemy's supplies and logistics
-Preventing the arrival of an important delivery

If they implement this feature now, they will push it further in later Arma game releases by adding destructible bridges and tunnels thus providing more strategic approaches in one single mission

I still don't understand why they are procrastinating.
The potential of fast roping will be shown in many scenarios :
*Jungle and forests
*Open caves (http://bit.ly/1MmtL85 )
*Urban environment :
-Insert troops in narrow streets
-Infiltrate buildings from rooftop
-Providing cover from rooftops
*Naval boarding (for instance anti-piracy boarding)

This could be a great challenging feature similar to the bipod in Marksmen DLC
There is some areas where you are not able deploy ropes like over :
-Dense area of trees
-Sharp slope
-Rough terrain
-Waterbody and so on ....
So you have to put a kind of a zone exclusion map for fast roping