Wargaming is already doing it with arty so they have shown they somewhat care. But with the normal tanks this will obviously be a much larger endeavor than just nerf damage.
Each type of ammo (AP, APCR, HEAT, HE) need to have clear uses that differentiate them. I will list what I think might be a good idea below but keep in mind that wargaming will most likely have to look at every veichle in the game and change ammo loadouts, armor, and health values depending on what works.
But I believe that this will be in the best interest and help the game health from just endless premium spam.
Vs Sloped Armor: Very good
Armor-Piercing Composite Ridgid (APCR)
Damage: Low (between 10-20% less damage compared to AP)
Penetration: Very high
Velocity: Very high
Vs sloped armor: Decent
High-Explosive Anti-Tank (HEAT)
Damage: High (between 10-20% more damage)
Vs sloped armor: Bad
-Also make it so it can't go through spaced armor at all, can still destroy tracks
Damage: Very high
Penetration: Very low
Velocity: Very slow
Vs sloped armor: n/a
If this is confusing ill try to explain what I'm trying to do here.
AP should be the go to round for most armor types, maybe make the normalization more extreme to emphasize its usefulness to slopes
APCR will be good for sniping moving targets or combating very thick armor plates that also have spaced armor and are somewhat sloped.
HEAT will be more of an opportunistic round, rewarding more damage but only good vs mostly flat armor and completely useless if used against any spaced armor such as skirts and tracks.
HE is mostly the same as it has its role in the game as seriously punishing lightly armored veichles if used properly.
This is just one idea to take this, but in general having ammo be dynamic and having to think was is the best for this situation will raise the skill ceiling rather then just hitting the 2 key.