Are you suggesting that anyone who denies the holocaust should be excommunicated? What about non-Catholics? What would happen to them?
Yes. Quite aside from the moral issue (denying the Holocaust amounts to bearing false witness against 16 million people), a blanket excommunication of all Holocaust deniers would send a message that the Vatican will not countenance the perversion of history by its members. This would have the not-incidental benefit of sending a message to the leaders of the Middle-east as well.
What about non-Catholics? What would happen to them?
Non-Catholics are obviously out of the Pope's chain-of-command, and therefore not his responsibility.
Shalom.