I did wonder to myself if the prologue would be the depiction of what exactly it is that happens to the fleet since that event per the synopsis is what kicks off the plot. But even if it was, and even if Cumberbatch is in that sequence his name doesn't have to be revealed at that stage.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist