Necrarchs don't get any special characters. I mostly play Von Carsteins myself, when I'm bringing vampires at all, but even I would have liked to have seen a more equitable distribution of special characters across the bloodlines.
That said, I still prefer leaving the bloodlines as fluff and voluntary army themes rather than a rigidly enforced rule structure. As a Carstein fan, I like that all of the bloodline traits are open, allowing me to build caster vamps following Mannfred's tradition or melee vamps following Konrad's tradition in the same army, something I couldn't do back when Bloodlines were a thing.
It's not like you can't build Necrarchs out of the basic vampire stats & traits. There are bloodline powers allowing for caster-oriented vamps. sadly, they're a bit overpriced & under-powered due to an overreaction to caster vamp dominance in 7th edition, but the pendulum effect is just the way of things with GW. Necrarch-style vamps dominated in 7th, now they've taken a hit in 8th, hopefully they'll be back in 9th.
Additionally, the new book added at least one new option specific to each of the classical vamp bloodlines, with the exception of the Blood Knights, who already had their own unit.
Strigoi (one of the big winners this time, which is fine by me, since they suffered the most under the previous book) got ghoul kings, crypt horrors, and terrorgheists to add to their varghulfs. Lahmia got the Coven Throne. Von Carsteins got Vargheists (although I personally feel they fit Strigoi or even Lahmia better) to add to their black coach and special characters.
Necrarchs have increased their reputation as skillful spirit binders with the Hexwraiths, an interesting and potentially quite effective special choice that calls out the NEcrarchs by name as the first to devise a means of binding this unit of ethereal cavalry. With their spirit binding skills specifically called out, banshees, wraiths, and spirit hosts take on added relevance for Necrarch themed lists. And, of course, there's the new Mortis Engine, buffing magic with its blasphemous tome and borne aloft by yet more ghostly spirits.
There's also some units that, while technically not Necrarch themed, can easily find a place in Necrarch lists if you look at them from the right perspective. While the terrorgheist is thematically more of a Strigoi thing, it provides you with a large flying undead monstrous rare choice to represent the monstrous necromantic constructs that were the bloodline's primary thematic element before the new ethereal theme. Nobody's going to begrudge you running that unridden zombie dragon from your long lost sublist as a terrorgheist.
Also Mannfred, while officially a Von Carstein character, looks and acts an awful lot like one would expect from a Necrarch character, and could provide a strong counts-as option for the Necrarchs. He can even ride an abyssal terror, making him a perfect stand in for that old Melkhior model. He was a cooler character than Nicodemus anyway.
It's not a great situation, I'll grant. I'm certainly hoping that Necrarchs get some more attention next time around (same with Lahmia and Blood Knights). But I don't think the current situation is that terrible, either, and I certainly wouldn't say that the Necrarchs, or any of the bloodlines, really, had been forgotten in the current book.