I wouldn't be surprised if Deans doesn't take a 5th prop, but does take a 3rd hooker and 4th lock.
Logic behind the no 5th prop is that he has a couple of guys who Deans probably thinks can cover both loosehead and tighthead in Kepu, Alexander and Slipper. Palmer or Ryan would've likely been the 5th prop (assuming Sio is considered too you and inexperienced), and they're both specialist tightheads. You could say that Slipper and Kepu are more tightheads than looseheads currently, and Alexander has mostly played at tighthead for the Wallabies.
Third scrumhalf? I reckon Deans won't take a third scrumhalf. If he was, then White would have been called up already, with Burgess to maybe follow later. Instead Deans is waiting on Burgess' availability (which I think is harsh on White, but that's another story). Although, it wouldn't surprise me if Deans ends up choosing Phipps, not because I agree, but because, well, it's Deans.
If it was a touring squad, though, you'd definitely have the 5 props, 3 hookers, 4 locks (or one backrow who is a genuine lock cover, moreso than Dennis) and 3 scrumhalves.
That will mean that the final makeup of 6 players to come in may also look like (along with who I expect Deans to select in brackets):
1 hooker (Hanson?)
1 lock (Douglas or MMM)
1 halfback (Burgess, Phipps or White)
1 centre (McCabe, otherwise A. Finger if McCabe is injured)
1 fullback / flyhalf cover (Beale, if Beale is out, maybe Cooper, but I really think Cooper won't be picked from here)
1 anything - can't second guess Deans here; could be the 5th prop, 3rd halfback (unlikely), or another wing/fullback if Beale is not available, like Mogg or Mitchell
The two least covered positions in the backline are 13 with just AAC (Adam Ashley-Cooper), and 10 with mainly JOC (James O'Connor) (as I doubt that Deans will put a debutant 10/12 at 10 when he has played at 12 all year bar one game, where he didn't shine, and, this is me surmising, Barnes is considered more of a 12 / 15). This implies to me that McCabe and Beale (if available) are certain selections.