Some new doctrines that will have lack of assault abilities, but add more support and manuever abilities for factions and make players more options for mixing and trying different doctrines combinations and their combat roles in PVP matches.
No much mobile artillery options like artillery do for other allies, soviets can build up static heavy artillery cannons wich are expensive and easy counterable - sometimes players just need to spot or drop recon flight on area and then use stuka drop bomb ability wich could not be counter by AA defense or somehow.
ZIS 3 and SU 76 abilities are deffinetely cant be called as artillery support.
I suggest adding more doctrines with Su122 - to soviets -fast, mid range artillery with medium armor
and hummel or wespe for axis - first one is long range, lightly armored and not so fast.
wespe - light, but fast, low silhouette with able to fire close to mid range artillery.
Maybe add to soviets some officer units, that can buff allies infantry or something like this.