for 40k i really hope the t'au faction gain more auxiliary models so that it has more options for it's unit composition and more lore for theses units since one of their main lore is that they have a lot of auxiliary units in their ranks
for the leagues of votaan they lack some walkers, some super heavys (hope something like a 4 legged mining equipement), some long range units (maybe mortars), some mele vehicles, more named character and a bit more infantery (one mele focused, one more support like neurotermagaunts but better, one shotgun like battleline)
in general sub factions for a lot of xenos races need sub faction units (ex. : mele focused battlesuits for the farsight enclave, more specialised wraith construct for craftworld lyaden, special loot wagoon like units and furtif units for the blood axes, more harvester like units for the more harvester focused necron dynastie, more unique organism like the nephilim king court strategy, special homoculumbus creation for certain dark eldar subfaction, ect...)
(also i hope one day genestealer cult get genestealer infected units from other xenos faction (F.E. : orks, eldar, tau) and more military special equipement because i think an army with most of their weapons being civilians equipement having almost the same stats as astra militarum weapons makes you question why the astra militarum is not using theses)