I was curious and so I did some digging about Ben Lucas and I'm not sure he's as good as everyone appears to be remembering / thinks he is.
Firstly, towards the end of his time at Montpellier he was struggling to even get on the bench for them, let alone start. While I do concede he was pushed out by some quality players - Jesse Mogg, François Steyn, Ruan Pienaar, and Nick White to name a few. He has come off a contract in Japan where he played for an average side (literally finished 8th out of 16).
Looking at his time there, of the 15 games he started only 3, none at 10. He had 4 appearances off the bench and 8 games where he wasn't in the 23.
So here is what we can see from the most recent evidence -- he isn't outstanding by French Standards; he isn't even outstanding by Japanese standards.
Given this track record; personally I don't think he'll be starting -- I'm not 100% on Daugunu or Perese at 15, but I think Daugunu has a decent shot (again assuming there aren't any players added to the squad). I would say at this point (from what I've seen) the likelihood of starting at 15 is 40/35/25 Daugunu/Lucas/Perese.
Obviously if Lance is signed he starts at 15 with Daugunu returning to 14. But I'm not sure there are too many scenarios where Lucas is too much more than a guy who can cover a lot of positions.
Also regarding the 'Who plays 10' question, I just don't think you dump Quade if your intention was anything other than starting Hamish Stewart. (I have been amazed at the ineptitude of Queensland Rugby in the past but SURELY you don't dump Quade for Stewart only to start Lace or even worse Lucas.