@Riot is the plan to slowly phase out MR/Armor shred? Just curious

was looking at Amumu's new passive on PBE and it got me thinking if perhaps the plan is to slowly phase out MR/Armor shred in favor of Increased Magic / Physical Damage? Perhaps the increased Magic damage side could be the AP equivalent to Lethality? (at least from where I see it) If the plan IS to eventually phase out MR/Armor shed and replace them with lethality/increase magic damage of some sort, what other champs do you expect to get similar changes?

I was thinking how Karthus's W shreds 15 MR to those who pass through the wall, and what it would look like if Riot decided to change it to instead make targets be dealt increased magic damage instead. Perhaps have it start at 5% increased damage and increase to 25% increased Magic damage as you level it up?

I dunno, I'm just contemplating how this would go. Thoughts?