Another old world article, this time explicitly about the tomb kings. Nehekhara under Settra extending all the way north to encompass most or all of the old world might be new lore - iirc back in the day tomb kings incursions north were mostly following after mortals who had stolen treasure from sleeping kingdoms and taken it back home with them, rather than aiming to reclaim territory that had once been theirs. But I could be wrong, that might be old lore, and even if it's not I'm cool with it as an addition.
Strong evidence in support of my theory that the old world undead presence will mainly be tomb kings rather than vampire counts - though the presence of tomb kings doesn't exclude the possibility of vampire counts also getting rules, models, or narrative focus. But while there might be rules support for vamps (old world was supposed to support all oldhammer factions, even if they're not a focus of the narrative), I again doubt they'll be a narrative focus. The game is set at the time of Magnus the Pious - there are vampires around, but the Von Carstein wars are over, Mannfred is deep in his bog mummy period, and barring retcon there just aren't any major vampiric uprisings going on in the old world at this time.
I also doubt we'll see much in the way of direct model support for old world vamp counts, because there just isn't a significant aesthetic difference between old world VC and AoS Gravelords, to the point that sales of one line would likely cannibalize the other. You could say that 30k and 40k both have marines, but marines have always gotten special treatment for sales reasons, and GW only really started pushing 30k plastic kits around the same time that new 40k marine releases started transitioning to the new armor mark with a significantly different design.
As for model support for Tomb Kings... I'd like to think so, especially since this this is a lot of emphasis on the faction fairly early in overall development for them to be an afterthought that has to wait for the game to be successful first to get any actual support, but I'm not sure. The current article would have been a great place to showcase some 3d design work on tomb kings bits & bobs if such were in the works, and we're still just seeing 2d art and maps.