That would still have the effect of the upgrade usually coming when T3 is built, which would give a huge sudden power spike (together with T-70) that should be avoided.
T4 is too late
Are we aware that when okw builds their first truck they get a huge power spike including a weapon upgrade, a snare, an hmgamd a light vehicle?
Or usf getting a free squad
The 7th man isn't the caliber of a weapon upgrade and I think you are overstating the power spike it would add. Again, make it a fuel unlock (like molitovs but actually something someone might unlock) so it doesn't effect anything unless the player wants it too, which is how all conscript upgrades should be applied. It locks out a weapon slot and cons 50mu,its not handed out and they are still conscripts. Some players want variety and a chance to not have to go T70 each. And. Ever. Game. 7 man conscripts and the halftrack could be alot of fun but is hardly viable due to the timing of the upgrade. What's more is that cons have been getting trashed for the whole game by that point because nobody was concerned about the power spikes of weapon upgrades and locking them behind the final tier