I just had a though.
What if the Tank version of Sheen and the Tank version of Spirit Stone.... are actually the same item?
I would imagine that the upgrade paths for spirit stone to have more general usefulness as an upgrade to help a niche item transition to late game usefulness for any jungle tank. They wouldn't want it building into an item that fits into a different niche. In other words, they aren't gonna build a tanky-melee-ability-spam niche item out of the mana-hungry-jungler niche item. There are certainly champs that fit both, but you are also hurting champs that only fit niche and not the other.