Right now you could only take simultaneous turns when you are near your ally. So you´re seeing them because you're together. If all players could move at the same time it's useful to know when the others are preparing a spell, a skill or something like that to avoid friendly fire. The "channelling" animation could help with that.
When the team member already cast the fireball, entangle, grease... while you are charging, it's not useful to see the animation and you already know because you´re already burning, or entangled. You want to know that he´s casting before you charge...
Or you want to know your teammate is dashing, or misty step near the enemies so you do not hit him/her.
I know in an ideal world the players will communicate before doing something but you know how MP is in real life. Right now in the portraits, there´s a big "crossing sword" indicating that you are in combat or out of combat, but nothing else that indicates what you`re doing.
OK, I see what you're saying. You want to see what another MP player is considering doing, even if they are uncertain and don't actually do it, to avoid possibility of self-harm.
So the way it currently works you and a team mate could actually be executing actions simultaneously? I guess I assumed that once one of you committed to an action, it would complete before any other team-mate could execute an action, avoiding the self-harm scenario while still allowing you to interleave actions.