Well, if you ask me, which none of you did, but I shall give you my opinion anyway, Reshiram and Zekrom are Dragon/-Fire and -Electric types, respectively, and if Kyurem really
is the revived corpse of the once combined Reshiram/Zekrom, then it only fits that it is a Dragon/Ice type because
a.) Death-->Cold-->Ice
b.) It is one of the trio types, like with Articuno, Zapdos and Moltres, and Raikou, Suicune and Entei (and although Suicune was a Water type, it's close enough and it learned naturally and was able to learn plenty of Ice-type moves.)
Grey also fits with this story. 'Cause grey is a dismal color. Kyurem is likely to be, if not the trio mediator/master/whatever, the link in the trio, from yang to nothing to yin and back again. And again. And again. AND to be the mascot for said Pokemon Grey.
And with the two unusable moves--Cold Flare and Freeze Bolt, I believe--they could be learned by Kyurem at level 100 when Reshiram and Zekrom learn their other signature moves, Blue Flame and Lightning Strike, and when, currently, Kyurem learns
nothing. Zip. Zilch. Nada. Nothing. Zero. Anyway. Yep.
And I have no comment on this "God Stone." I have too much on my mind. Figure that one out yourselves.
If you think you're safe after you've beaten the Champion again...