I think there is a general consensus about T4 being too late for this. T3 seems reasonable.
The danger in that is that it would instantly give T3 a huge power spike, as it also gives the T-70 and Soviets can usually float enough munitions to instantly upgrade all their Cons squads.
I don't really see T3 happening unless it's a global upgrade or unlock (side tech) that has its own MP/FU cost and build time, so it would come at tier "3.5". With T4 giving it for free like now.