What IF only the champion point +% bonus to stats after spending 100 CP and tree passives were available to character within Cyrodiil, Battlegrounds, or Imperial City? I.e. Battle Spirit blocked the node bonuses for a more universal campaign environment. In lieu, the 10/30/75/120 CP tree passives could offer different choices i.e. pvp or pve oriented passives that would be active in player-verse-player content.
Considering this "What IF," may bring player-verse-player more towards gear/skill choice builds. Much like character builds specific for non-CP campaigns and battlegrounds except you retain the increased stats and CP passives i.e. the following: Field Physician, Infusion, Revival, Determination, Spell Absorption, Bulwark, Critical Leech, Unchained, Invigorating Bash, Phase, Resilent, Reinforced, Opportunist, Perfect Strike, Exploiter, Last Stand, Vengeance, Spell Precision, Foresight, Arcane Well, Retaliation, Riposte, Butcher, Tactician, Ensnare, Inspiration Boost, Mara's Gift, War Mount, Plentiful Harvest, Synergizer, Master Gatherer, Wind Running, Fortune Seeker, Merchant Favored, Treasure Hunter, and Shadowstrike.
Introduce new champion point passives specific for player-verse-player. For instance, the passives Inspiration Boost, Master Gatherer, etc. could have alternates. The big "What If" here rescales open world PVP and Battlegrounds without direct CP nodes bonuses. This does not directly penalize either sides in context to promoting an environment for both PVP/PVE content users.
Alternatively, What IF, ZOS introduced a "Battle Spirit" champion point tree that would be active only for PVP content and game play i.e. duels. A player character can redistribute their points in or out anytime without impacting their performance in either one. Would this be a viable option for you?