Delixe: I wouldn't put it past North Korea to develop torpedoes with nuclear warheads. They are far cheaper to make than ICBM's, they would be devastating against coastal ports and they have the dubious benefit of potentially causing a Tsunami which would cause even more devastation. The only reason no-one else uses them is the potential for colateral damage but I don't think Kim would be too fussed about that.
The issue is more getting a nuclear warhead of sufficient size. We have no real knowledge of their capabilities, but given they have only tested recently, I would say their bombs are currently far too large to be considering such a small delivery system.
This is why they develop large rockets. If they could make small warheads I would expect them to use an artillery based system instead (as I expect they have developed for their chemical weapons systems).
On a slightly different note, given they apparently killed 46 sailors, should their football team be excluded from the World Cup? Or should we keep sport and politics very separate?