There's multiplayer and then there's multiplayer.
It's pretty obvious how cooperative multiplayer can work, with a campaign that multiple players progress through together, with shared save games and the ability for players to join and leave the campaign while in progress. This is a solved problem if the number of players are few, you could basically copy what Nintendo did with the Mario games.
But it's not obvious to me how to do competitive multiplayer without hurting immersion, because you're always aware that you're competing with other people in the real world, and the game is just a battleground. I don't know how I could get immersed in a game world full of e-sport trappings like guilds, clans, tournaments, rankings and stats.