I don't think they will turn Death into a death knights faction that would more likely alinate death players considering they have been waiting so long for a release and gameplay wise in my eyes is redundant if I wanted that I would play stormcast or chaos. As alec said the overhaul already happened.
"The design of nagash's staff alkanash, harks back to his past as a high priest of khemri, with motifs from both the tomb kings and vampire counts used in the final design"
"Nagash is a landmark minature for several reasons. He enabled us, as a design team, to re-imagine the undead range and create a new aesthetic for undead characters such as Arkhan and neferata."
Another part
"Being able to create nagash enabled us to redefine the undead range, to establish a new ruling class with a grim aesthetic.
Considering they released Flesh eater courts and their lore is no where near PG 13 if you actually read the battletome I think we have nothing to worry about. I do think the new undead zombies, skeletons etc will match how nagash and the mortarch's look on facebook people have been constantly begging GW to release new zombies they said they passed our feedback on.
The new warhammer underworlds has been giving hints on the direction they are going with Death.
As been said the reason why they kept the VC stuff I do agree because they don't look "historically" accurate like the tomb kings I could easily see the undead wearing the mask for the warhammer underworlds poster to be a new "liche priest" they look more gothic and grim and clearly does not just only look like an undead Egyptian skeleton.
Anyway... before we go off topic again I made a thread about this.