Deploy Available Builders in Raids
I did not see this listed in the exhaustive list of feature requests and rejected suggestions, so please forgive me if I missed it.
The idea is fairly simple. If a player has builders that are not currently working, then any free builders can be deployed in raids to raid obstacles like trees, rocks and gem boxes. The possible gem rewards would be the same as when you remove obstacles from your own map. Builders are not soldiers, so they would be incredibly weak, and if knocked out in action, they would require a nap, like the barbarian king, except perhaps somewhat longer, during which time they would not be available for building or raiding.