I would be fine with them increasing the amount of magic pen on the boots. That way people really have to decide on whether or not getting magic pen will help you versus CDR or Tenacity on a CC heavy team.
I mean, it'd only need to be increase to 20 from 15. Or make the cost of these boots lower.
OR better yet. Actually change the passive so it's more interesting.
Sorcerer Boots: 45 movement speed
Unique Passive (Shadow Magic): Basic attacks and spells now apply a debuff to enemy champions. Enemy champions have their magic resistance reduced by 5 + 2% per hit. (Stacks 2/3/4 times based on level. DoT spells only apply one stack).
That way they aren't too good of a buy at early levels for some champs (Brand) and scale later for other champions who struggle with pen that can't buy other options. Also, it forces AP champions to actually use their skills and basics so they can't insta-gib someone if they didn't try to get max stacks.