In my opinion no one, including Dino, knows what we have in Garrett Shrader. Shrader's greatest asset, what would really set him apart from TD, can only be demonstrated in a live, full-contact football environment. That is why Shrader deserves to see the field. He has been good enough to challenge Tommy without being able to show his pocket presence, escapability and running ability in a full-contact situation.
Remember years ago, the grad transfer QB Drew Allen (I think that was his name) was the starter early in the season? He just wasn't moving the offence and Terrell Hunt replaced him in a game and wowed everyone with his dual-threat ability. After the game Schaeffer said that Hunt had never shown that ability in practice. Of course not, you can only show that in live action. That's why GS should be given a chance to show fully what he could bring to this team on the field. A fair evaluation of a dual-threat QB must include seeing him in a full-contact environment.
As mentioned multiple times above, Dino is fighting for his job so I do believe he will put him into a game soon because I think he also wants to see exactly what he has in Shrader. I trust him enough to defer to his judgement as to when that should occur.