Spell vamp and mage resist

I have always thought that it was incredibly difficult to itemize for magic resistance. You can, but you sacrifice majorly for it. The maximum you can get on one item is the portal, which does come with 60 defense as well and is great for sieging, and I do frequently get this. However, I am at a much greater disadvantage as a tank against a primarily magic damage team than an AD team, as it is easy to itemize lots of armor and lots of health. In face the champions that come out most ahead in terms of late game itemization, all else being equal, tend to be the AP tanks to my reckoning. Amumu, for example, can stack lots of health for cinderhulk passive and be nigh on unkillable while still having Liandry's and Rylais, for basically a 5-7% ps melt with his W after resistances. I have 1v1d Nasus late game as Amumu. Same story with Chogath, the items are just way too supportive of these AP tanks and they tend to bring so much utility that actually shutting them down or getting team fight control with Cho, Amumu, Ekko, Volibear, or any champ that stacks armor + health and has utility ends up being very, very difficult.

We do have armor pen items, but they come at a great cost. LW is 30 less damage than void, and granted it's sustained damage, but it's not really sustained if you would only have enough time to get a full rotation off as a caster (maybe) against a rushing Volibear.

I believe the difference may lie in the difference in lifesteal capabilities between the two kinds of damage, so I would propose something along the lines of bringing more spell vamp opportunities into the game (we only have what, 2 fully built items that have it and it's not a very astounding amount at that, especially considering the difference between aoe and single target), and also more magic resistance.

This would give us the edge we need to square off against moderate-dps utility tanks who do a lot of AP damage, while not completely neutering their team fight presence by improving their siege in exchange for damage.

I think this may be a good alternative to the incoming nerf for Eve as well, though I recognize it is already in the works so it could at least mitigate the changes you were going to make. As of right now champs like Swain, Cho, Amumu, Taric, Blitzcrank, Fiddle, And maybe even Jax in this category just shut down fun if they get too far ahead. I think for some better itemization against AP we'll have more diverse strategies, and it would give you the room that you need to tinker with AP casters' kits without too much of a rework power swing. Maybe we might even see Ryze again.