Honestly, i usually hate silent MCs, with one big Exception: Adol Chrisitn, whose Adventure i have been following for 7 games, and thus, while being silent, there's a Character to him due to his actions, his Interactions with the World and the Characters
Will Byleth be like that? Dunno, we will have to see. I just hope we don't get blank face during emotional moments ala Pokemon Sun & Moon. That was pretty damn annoying.
Atleast he won't be Corrin 2.0 that way.