I would like a window in the garage that would show the next milestones I can work on in a game session.
Example :
IS-3 needs 2000xp to get 122mm BL-9 (approx. 4 games)
T28 needs 2300xp to get the SCR 528 (approx. 5 games)
E 75 Commander needs 19% to get repair skill
...
BDR G1 B is at 84% Mark of Excellence
You could also show an estimate of the number of games to play to achieve the goal.
This way a player could focus his efforts on a tank in a given session of play.