Pious,
The difference being that the MRA4 already has the pylons, wiring and software installed - I believe it is already "capable" of dropping most stores in the NATO inventory. It is thus already much further down the line (especially cost wise) than the C-130 you picture as an alternative. It was designed to do this stuff from the outset....hence the "A" in MRA4.
As has been pointed out, carriage and release trials haven't been done for anything other than ASW weapons (to the best of my limited knowledge?), due to a lack of time, money and probably intended useage by the RAF.....
Jayand,
As I see it, in this era of belt tightening the RAF can't afford to keep an airfield open for 9 aircraft. Therefore either more assets need to be moved to Kinloss (and I don't mean 2 yellow helicopters) or the MRA4 (if we get them) need to move elsewhere. However, that is just my personal opinion. Closing a base also doesn't save money in the short/medium term - try following the discussions on Lyneham closure and the move to Brize on another thread.....