At the start of the mustering phase, a prompt asks players if they want simultaneous or turn-based mustering. Mustering will be simultaneous if consent is unanimous. A muster conflict (such as two people being able to muster into the same sea) forces turn-based mustering.
I believe that simultaneous mustering, that is, all players mustering at the same time should be default on thronemaster, as opposed to mustering in turn order. I know this technically isn't how the rules say to do it, but I really believe it would speed up live and PBEM games substantially.
In general, this is how most people play the board game (in my experience), and 95% of the time, what I choose to muster won't be affected by other player's choices. I believe this suggestion strikes the right balance, by allowing players to choose turn-based when it matters, and simultaneous when it doesn't
thoughts?