No doubt there will be an argument between the US and China over who'll get to mine the asteroid.
EDIT: In all seriousness though, it's about time something like this was set up in order to co-ordinate the worlds military and space forces to combat a potential NEO threat and since the UN is probably the only major global co-ordinating force it makes sense to route it through the UN rather than set up another body to deal with it. So long as they don't use North Korean launch vehicles then we should be alright...