Without getting too into details..
Geneva convention = treatment of Prisoners of War....it mentions use of weapons also, but in reference to use against prisoners.
Hague IV = rules of war.... it does not restrict weapons by specific caliber or type of round. It instead says that projectiles "calculated" to inflict excessive damage is illegal.
This is why many countries opt for the cheaper FMJ instead of JHP or other rounds. Use of large caliber machine guns against personnel was considered illegal when Armies specifically calculated the use of such large projectiles against belligerants. It is a matter of either NATO policy or the specific Army's policy.. not the Hague..and definately not the Geneva convention.
Enough of that. Jane's is a source that most of us soldiers reference when we aren't in the loop. Janes is usually right on target. XM8 may serve it's purpose by showcasing new concepts and materials in weaponry. Making it the mainstay of US forces may turn out to be too big of a step. Regardless, most of us aren't in that big of a hurry for a new rifle. A better caliber round is a good combat option.. but costly in training. Think maybe the higher caliber round would be a good option for specific positions in the firesquad, or maybe a specific kind of fire team?