This is an idea that will only work . . .

. . . if you have complete air superiority. In other words, it's something only the USAF can actively consider:

The U.S. Air Force is now thinking about turning its C-17 transport into a bomber. In the last few years, the JDAM (satellite guided smart bomb) has made aerial bombing far more effective. Because of the satellite guidance (GPS), aircraft can drop the bomb from any altitude, and still get the same accuracy. Thus bombers can stay high, out of range of ground fire. That got people, inside and outside the air force, thinking about using transports, like the C-17, as bombers. Transports are equipped to drop heavy equipment, mounted on pallets, by parachute. It would be a simple matter to have smart bombs, on small pallets, shoved out the rear of C-17s (or C-130s, Etc.) This proposal upset the air force generals, most of whom are combat pilots. So the idea never went far, until now.

If you're in the unique position of the USAF, where air superiority is pretty much a default condition, this is a potentially brilliant notion. For less dominant air forces, it's just not remotely feasible to use slow, heavy transport planes for any kind of combat role.

Hat tip to Dennis Huff for posting a summary to the TacOps list.