Been hearing rumors of 3 planned Supplements for the Nids with Leviathan, Kraken and Behemoth being most likely. Though it may just be a large digital Dataslate (akin to what we saw with Cypher)
Probably wishful thinking but maybe we get some alternate biomorph selections with each supplement.
Perhaps something to give +1-2 Toughness or +1 Armor, but you are restricted from choosing the Biomorphs from core codex(as was done with Farsight codex). An additional set of Bio-artifacts or alternate Warlord table are also all standard supplement fare.
Perhaps a profile for changing one Genestealer Brood in the detachment into Ymargl