I have a sincere question about the item shop
why is there no magic penetration based item with attack damage stats?
there are pure attack damage based champions that deal magic based damage, yet their damage cannot penetrate due to there not being any items for these champions to buy. two examples that come to mind are kindred and kayn.
one COULD argue that buying wits end can help, but the reality of it is that wits end does not help. at best you can buy sorcerers boots and somewhat deal magic damage to champions if they havent built a lot of magic resist. to that end using abilities that deal magic damage on pure attack damage champions leaves little use except for when paired with champions who can reduce magic resist like morgana or against minions.
then there are a large quantity of champions that have both attack damage and ability power numbers in their kits and deal both physical and magical damage. tristana kayle akali and katarina come to mind.
can we have a %magic penetration version of last whisper or something?
builds 
and 
as his core build. But he actually has some AP scaling, so it's a valid buy.
There are now some champs not so lucky.
And I can see how in some specific niche situations you would want to buy it without the AP being such a waste. Especially now that some runes will provide AD or AP depending on what you already bought.