This may not be as 'slight' as you assume...
I was playing around with it last night. At first I thought it would be a few simple changes to Sprite_Battler. Possibly using the .hidden property of the sprite, but that also gets used to determine if the battler is "active". So I looked at using opacity of the sprite, but there are other things going on ("appear", "collapse", etc..) that use the opacity. Looks like it's going to take a re-write of the Sprite_Battler class, as well as some of the functionality of Scene_Battle (phase 4).
Do you also want to change the order that things happen? Now during the command phase you select the action for each actor, then during the action phase the actions are displayed. It sounds like you want to do the command then action phase for one actor, then go to the command phase for the next actor.