I'm waiting for the Rated R version....
I haven't heard one official thing about it being re-rated... and it is now finished I think. The added scenes I know of are not even in the fight sequences. They are in the Shire and in Lothlorien... So I am not sure where they could find a reason for an R.
I hope you aren't disapointed if your rumor turns out to be false, they lopped the guy's head off already... What more do you want? :~D
lordoftherings.net says that the extended version will not be R rated after all, just PG-13.