So basically a pack mule. Something in relation to the herder/trapper class in order to get something like that. Might be interesting, although don’t know how well it would work.
What I mean is, right now you can place a chest or storage item near the excavation, and then move it when full. To have a mobile chest like thing… sounds nice, but unsure how the actual behavior would be.
We probably would need an escort option in military for something like that, so we could have some kind of protection of individual targets; basically following the target around in I guess a sort of guard mode, and only breaking free to attack incoming attack near them.
The reason I mention that is due to how would the be “placed” at destination? If it were done so like an object, then you mind as well use the already existing storage items. Else it would be more like who will lead it, since we don’t have that kind of control over citizens, but have partial guidance upon military; which leads me to the “Escort” function I mentioned.
Unfortunately we don’t have that function, but would be nice, and would make this idea a bit more feasible.
Note: I try to make mining operations as close as possible or have something to trade, if not both; for those times playing RC so much. My trade instinct goes well with that faction. Have a decent desert seed just for that occasion. 
Regardless it is an interesting idea, I think. Like the concept, but it is more of matter figuring a feasible way to go about the concept. Reason I put an addition to yours. 