There is probably not gonna be shield grenade. The MNF spot was not made by bungie. It was more to get people excited. In one vid they said that in the alpha test there was 4 greandes (plasma, frag, spike and other) they had no idea of the last one but they ran a photo comparison and said it was not the shield grenade
i dont think they will have it becuase it sucks. All it can do is block a grenade or wraith shot. If your yousing it against people you just have to stand there and wait for it to turn off and they will be there waiting for you and then blow your head off. so its pointless, unless its in campaign then it will be good.