New single player mode: Defense
Along with being able to attack the goblins. What about defended against them? Create a new base (or copy layout) to defend against goblins waves. Created base for defended against goblets would be a seperatebroom layout similar to war base. Rewards could be loot/gems etc. alse a new achievement could be added in association with this defense mode.
Edit*
Instead of using current townhall items you have, defense mode would give you a certain amount of resource to use such as walls,def,th, etc to place.