I had thought spellbook would be the one to go
But I truly believe it's time that Riot seriously consider the 100% COMPLETE REMOVAL of the kleptomancy rune with NO chance of return.
Thankfully, given the very creative nature of the inspiration true, I'm sure it wouldn't be out of the realm of possibility to craft other "rule-breaking" keystones to replace kleptomancy's departure. Rule-breaking isn't necessarily bad (I think spellbook is a pretty decent keystone), but unfettered RNG has proven itself to be a balance nightmare. Is the GP going to get an elixir of skill and 2 mana pots to keep bashing my fucking head in, or is he going to get 4 bags of gold and come back with a sheen when I onl have a ruby, or is he just going to get a couple of stealth wards and get steamrolled the fuck over because he has a useless keystone? You see the problem here?
Like I said, inspiration tree by its very nature leaves a lot of room for experimentation, so let's just agree that the klepto experiment failed.