My problem here is that I cannot see how he would make both types of gameplay as compelling as a single-player experience for those who want it and as a multiplayer/MMO experience for those who want that.
There are things I like in my single-player games(cohesive story, goals, focus on my actions as the main protagonist, meaningful choices) that cannot work in multiplayer very well.
Likewise, there are things that people would expect from multiplayer(team oriented objectives, PVP, a universe that lets all players have an equal impact, huge battles that will take multiple players to win, guilds, etc.) that don't have much value to a single player experience.
I find it very hard to believe that the two can just coexist within the scope of one game, unless one part of it is squarely focused on single or multi at the expense of the other.