If we're getting Mono-gods, Cathay and Kislev as core on release, that'd be 1 LL per god and 2 for Kislev and Cathay...with 1 left over.
Who could that 1 be?
The one who is very ancient and in need of a champion to gain absolute power?
I've always thought he'll be the Attila of Warhammer 3.
Edit: everyone brought Be'lakor to my attention as the most likely candidate which I agree with. That explains the 'champion' part of the quote far better. I just didn't consider it because I figured 5 core Chaos factions would be overkill. I do think we'll see Nagash sometime soon though, it's inevitable. His importance and role as an Attila-like figure may not happen like we'd imagine since CA said they aren't doing End Times with WH3.