Ost could use another infantry option and a light tank.
Sov already has such a wide unit spectrum, that its more difficult to anticipate future units that would fill gaps, as their structure, with the directional teching and doctrine options, already accounts for most battlefield roles, depending on player choices. I expect Sov additions will come more in the form of doctrinal diversification of the existing unit roster for abilities and upgrades.
the early P4 model?
doctrinal PG's with camoflauge named 'Stormtroopers'?
Osttruppen doctrinal unit with Mp40's?
(as a call in, like guards, not with relief infantry)