Itemization why don't we?
Not entirely sure the implications behind having this work or what it may cause, however wouldn't it be easier to limit champions only to items that pertain to there role as riot intended? I know that this may take out some of the unique or customization factor. However I feel that balancing this season has been more hard than it has ever been before and from what it sounds like after every rioter post I read. For instance and this is a poor example (if someone has something better please let me know) Devourer's overall is a pretty unique idea, however there a few champions that can continuously abuse this item due to there mechanics. If riot was to prevent yi from being able to build that, it would still be a useful items to other champions, but no make yi redicously strong late game.
Note: having a somewhat hard time explaining this, hopefully someone gets the gist of what i'm saying.