Adam and Alex are busy packing for BlizzCon, so I've sneaked into the Queue offices to answer some questions this evening. There's no consistent theme here, folks; we're all over the map today with BlizzCon, lore, and player textures. If you don't see your question here, I still have a few in mind from the last post to answer tomorrow.
There are 3 historical scenarios that can be found in Yogg-Saron's "brain room"...What is the Shadow Vault event? I would guess that it is something as important lore-wise as the (other) two, but I have no idea.
It's widely believed that the Shadow Vault "memory" depicts a very recent and very unfortunate occurrence that took place (without player knowledge) after the Wrath Gate event. The NPCs in question are thought to be the souls/spirits/incorporeal whatsamajiggies of Saurfang the Younger and Bolvar Fordragon, who perished in the fight, victim to the Lich King and the Royal Apothecary Society respectively. The Wrath Gate cinematic implies that the Arthas has at least Saurfang's soul to toy with (which would explain the Orcish Turned Champion), but the identity of the Immolated Champion is less clear. Bolvar is by far the most likely possibility -- after all, the Immolated Champion is wearing the same armor Bolvar wore going to his death -- but nothing's been confirmed. Bottom line? Expect to see both Saurfang and Bolvar show up in the Icecrown Citadel raid in some capacity.