They intend to nerf tanky dps with this change however that will not work because values closer to zero give higher dps returns. Here is an example.
50 pen +50% vs 100 armour - Old = 25, new = zero
50 pen +50% vs 200 armour - Old = 75, new = 50
In this case it is a buff to tanky dps, nerf to everything else. However.
100 pen +50% vs 100 armour - old = zero, new = zero
100 pen +50% vs 200 armour - old = 50, new = zero
It is a nerf to tanky dps in situations where true damage was being dealt in the first place. But do we really want to nerf tanky dps by having everyone do true damage to everything? It'd rather they just nerf lifesteal so champions can't get 1/2 their hp back from a crit.