@Dysprosium Over on the Mystic Enchants forum I made a post titled "Zookeeper" asking exactly for this, a Legendary RE that removes the 1-pet restriction (but nerfs player-based dmg in exchange for balance)
All I want is a Diablo II necromancer-style char, where I have an army of pets at my command while I sit back and Curse enemies to boost their dmg.
I came close in Season 7 - I had no Permanent pets, but I was able to summon multiple pets via Infernal, Treants(with the +3 treant RE) and Hand of Gul'dan to spawn imps, and it did okay dps with a Boomkin build backing it up. Just a shame that Water Ele, Treants, all the Tame pet types, Shadow Fiend etc all share that slot (Which some did NOT in Retail - treants were considered summons, not actual pets with hotbars and should never take a pet slot, they're functionally the same as Wild Imps from Hand of Gul'dan)