A lot of raiding bosses in classic go down fast after they're released. Even the ones that "require" resistance gear. Will any bosses in Naxxramas be difficult at release? I remember Patchwerk being a simple boss tactics wise, but had a very high gear requirement due to his high health, damage, and short enrage timer. Then there's Sapphiron and the "need" for frost resistance gear. The 4 horsemen required many tanks. I don't expect Kel'thuzad to be much of a problem though.