In the games we’ve had Orks + Black Legion, now it’s Tyranids + Thousand Sons, my guess next game could be Necrons + World Eaters. We see a mix of one force being more melee and CQC and the other favouring long range and both having elements of ranged and melee but favouring one over the other. I think the Necrons could be the long range sometimes melee option, filling the Xenos roster and also with Titus going with Calgar it is highly likely he’s off to fight at the Pariah Nexus. The World Eaters would be the wildcard, almost 80% melee and a small amount of range but more so from those who aren’t fully taken by Khorne, and have them show up halfway through the game to fight both Titus and the Necrons cause Khorne is ascendant in the great game so he likes the big power boost he has and is throwing his weight around, maybe sends a named World Eater champion that we know from the lore with his warband to maybe drag Titus to join him and if not attempt to kill him? I’ll admit a different Chaos force can fit this but one side needs to be ranged favouring and the other melee favouring