I have my fingers crossed that that was PJ's idea of a joke. It's probably wishing for too much, I know.....
Another example of something that doesn't need to be done but is being done anyway. Nevertheless, it could work, depending on how it's handled. If it's a straight fight then it would be stupid as the Dwarves and Bilbo would all be incinerated-as least one of them would die in reality. If it's the Dwarves hiding under ledges, trying to avoid the fire and retaliating with whatever means they have available to them, then it could make a fairly good climax, provided that they eventually retreat into the secret door as in the book.
I can vaguely understand why PJ wants a confrontation between the main protagonists and the primary antagonist-particularly for the sake of Thorin confronting the embodiment of everything standing between him and glory. It's an interesting parallel in a way, since Thorin is of course susceptible to his own greed just as the dragon is.
This would be the solution to the problem that I have often wondered about: how would you keep non-book readers interested if Smaug, the big baddie, is killed off in the second film? Some of the "Normal" viewers as such may think "Hmmph, what's the point of watching the third film if the big baddies just died? We know the goodies are going to win now!" Obviously if he dies in the third film that problem is solved, though I do hope that he dies in his proper place, because his presence at the Battle of Five Armies as some have speculated would be plain disrespectful.
Again, not necessary really. Did the Fellowship ever have to have a full-on battle with Sauron? Nope, they didn't, even if Aragorn came close to having a slug fest with Old Nine Fingers during the Black Gate sequence.