Bird at lock also introduces an interesting question about the bench. I think we'd all assume a four prop rotation is May, Klemmer, Pole and Hunt in some order, and that Koroisau is no longer an 80 minute hooker except in emergency so Da Silva likely takes the third bench spot (or Latu Fainu as a more versatile 14 - personally I'd go Da Silva as you should have the best sub for the switch you know you're going to make rather than the one you're worried you might have to).
But if Bird starts at 13 there's no way he's playing 80 minutes, either. And replacing him with a prop is going to be a jarring tactical switch not to mention being the opposite of what you'd assume you'd be wanting to do - ie bringing on smaller guy to exploit fatigue. The idea of getting on top up front in the first 25-30 minutes then chucking Twal out there at 13 would be bizarre.
I guess this means Matamua would have the inside line on the fourth bench spot, unless we want to be hyper aggressive and name Latu Fainu and Da Silva on the bench. To your point, we're pretty exposed depth-wise because the obvious cover for an edge would be Bird and after that there's really not much for 11, 12 or 13.
Going back on myself slightly, maybe one option would be to start a big unit at 13 - presumably Pole or conceivably even Hunt - and aim to batter the oppo for the first 20 minutes, before bringing on Bird for the rest of the game.