Impossible to say, as you have no way of knowing how much input he had as Vieira's assistant. No harm in giving him until the end of the season to show if he's any better or just more of the same without the aura of being a world class player. Vieira didn't strike me as someone who would really put anyone elses opinion before his own, so I'd be surprised if Davies had much of a say towards the more baffling choice made.
I'm with you on this one. Might as well look at it as an interim basis and if he's successful then you can look into extending it, if not or if there is a change of manager for the senior squad then maybe our new manager will appoint someone himself.