GW adding those TK units to the GA:death tells me they want to make them somewhat relevant again. if you look at the sculpts of some of them, they still look amazing, and completely on pair with even the latest releases: necro/warsphinx, necropolis. Screaming skull catapult is a wierd addition tho, since the model looks like a bad joke. Settra is basically a finnancial treasure waiting to be exploited by GW. The model is old ofc, but they can easely make a new updated version of him, and essentially add a new "god" for Death. Or he becomes one of Nagash´s underlings tho quite unlikely since he doesnt kneel and stuff but yeah..
Tomb Kings as we knew them will never be back (probably), just like most other races just arent the same as in WHFB. But the concept of undead egyptians still sells, and death just happens to be in quite a need of some sort of expansion. Plus the demand of well TK is still here, alot of people want them back or remade. I honestly think the signs are too clear to ignore, something for death is in the making, and i pray its atleast 1% reminiscent of what TK was