I still think focusing on costs and effects rather than spells and abilities is the way to go. By forbidding all costs that need discard we shut down all activated abilities (like Survival of the Fittest or Putrid Imp) and spells with additional costs (like Firestorm or Devastating Dreams), which if I understood Eternal Shepherd correctly is part of the plan. Then we could decide if we want to forbid all effects that include discard among other things or just those that force only discard.