Of the other suggestions you mentioned, I could see a few of the following as potential swaps: Rites of Flourishing could possibly replace Horn of Greed as a 1:1 CMC swap & some extra land drops
This is to activate or deactivate its abilities
Grim lets you play a six drop on turn three and that will randomly ruin a lot of games
Outside of decks with topdeck manipulation or, to be honest, decks with Commanders like Aminatou I dont know if Id play this before Brilliant Restoration, or if I had one, obviously a copy of Replenish
Custom Handmade Edward Kenway proxies made from real Magic the Gathering card with many different alternated arts available for purchase.
I already consider Legions Landing to be one of the best white one-drops for Cube, so moving towards a higher volume of one-power creatures instead of Savannah Lions doesnt seem all that difficult