On screwing AP midlaners, it is easy to look at that list and think "Fuck... Every AP item costs 200 gold more...", but ignoring Zhonya's as an outlier, consider the old ADC items too.
They were almost always IE, SS/PD, LW, BT/BotRK, situational defensive/semi defensive item.
I can't be bothered to do proper mathematics, so very rough, inaccurate values will be produces, but it should give an idea of the changes.
IE is losing 15 AD (540g worth of stats) and 300 gold. Net change =-240 gold value. This is increased (I don't know how significantly) when we think of how crit scales with AD.
BT is losing 5 AD and gaining 200 gold = -218 gold value.
BotRK is gaining 200 gold and losing 2% HP damage on hit = -2xx gold value. Unique passives are hard...
SS is actually probably a buff overall in the late game, but the 50 reduced damage on proc will make a difference early.
PD is losing 15% AS, 5% Crit and 5% movement speed in exchange for 100 gold, a damage reduction passive and in combat mobility.
It is hard to determine the value of the unique passives, but my guess is a small net nerf
The new LW items are gaining 200 gold and a significant amount of armour penetration against tanks and squishies alike. I don't know the value of the new passive or the armour penetration but I am guessing that like the rest of them it is about 200 gold worse off.
The new marksman items look really good, but check the gold efficiencies. Most of the items are just over 200 gold worse off than current items. There are a few outliers - new Maw and Mercurial - but in general, everything is worse.
So yes, AP champions are screwed... But actually so are almost all champions. Of course, some will benefit from the changes, some will lose more, but that is true of every preseason. The average AP midlaner won't actually be worse off compared to the other champions in the game.