With new factions getting fleshed out with "completed" rosters (4 LL and RoR) and 4 LL promised for each of the starting factions; I've noticed a trend with the available Lords that shows a clear design path in terms of gameplay differences between each. Looking at how it relates to each faction and can help predict possible LL in the future.
Each faction seems to be built around having different roles being filled by 3 of the LL and a fourth that is similar to another with a few changes.
In the case of the High Elves we have:
A pure melee lord, a dedicated caster, and a ranged sniper/assassin. The fourth lord is another caster that focuses on supporting magic rather than offense.
The Tomb Kings have: a full caster, an assassin, and 2 hybrid lords that buff different aspects of their own army.
Using this idea that each lord should vary somewhat from each other, we can predict other factions such as the Dark Elves FLC Lord: we have a hybrid lord, a caster, and an anti infantry blender. If the fourth lord is Lohkir Fellheart using vampire coast mechanics, he would fit as an assassin.
If we take what we know and apply this logic to the vampire coast, so far we have: a melee/ranged specialist, a (supposed) hybrid lord, and Saltspyte is most likely a assassin or anti infantry. The fourth lord would most likely be a full caster to round out the rest. Based on the silhouette I believe they are a syreen lord with the new lore of the depths and the syreen heroes have become casters as well while the melee variant is now just a unit.
Sorry for the long read, have an imaginary cookie.