I actually suggest a crazy idea in another thread to switch T-34 with SU-76 making T3 all about light vehicles and making soviet T4 similar to US T4, I though about keeping the early game the same but making T4 unlocked only after you got 2 tech buildings up.
I made a similar suggestion some time ago, with the difference that you could still go straight to t4 after t1 or t2, but t3 would be only half the fuel cost of t4, like motorpool was in coh1.
It seems that many would rather switch su-76 with t70 instead, which I guess wouldn´t be that bad either. But something has to be done to make t3 or t4 more attractive compared to just waiting for call-ins.