People on a game forum would rather destroy gaming, than allow co-op in games. Multiplayer can be implemented discretely - Final Fantasy 6 had multiplayer, you can set party members to other controllers. Mario Maker has multiplayer. Asynchronous multiplayer or multiplayer implemented in ways that are non-intrusive would make more people happy.
But forcing an open world into every game? Just thinking of some genres that would be ruined: 4X, Visual Novels, dungeon crawlers, Linear Story Experiences, Collectable Card Games, Roguelikes? You can make those all multiplayer (Co-op player votes on responses with main host, Co-op player controls an aspect of the game, co-op player makes decisions, plays with you as a team mate) with little to no impact on the actual game.
But forcing an open world into every game? Just thinking of some genres that would be ruined: 4X, Visual Novels, dungeon crawlers, Linear Story Experiences, Collectable Card Games, Roguelikes? You can make those all multiplayer (Co-op player votes on responses with main host, Co-op player controls an aspect of the game, co-op player makes decisions, plays with you as a team mate) with little to no impact on the actual game.