Rough translation of the article mentioning this.
"Tuesday, July 13th, the director and RioFilme's CEO, Sérgio Leão Sá posted on Twitter that parts of Breaking Dawn could be filmed in Rio de Janeiro. Robert Pattinson even commented that he'd love to come to the city."
Sérgio posted around 10AM: "RioFilme, SEC and Rio Film Commission are working on the 4th movie of the Twilight Saga to be shoot in Rio".
UPDATE: He just tweeted: Paris Filmes, Brazilian distributor of Summit's movies, is also helping us negotiating part of Breaking Dawn to be filmed in Rio"
How's that for authenticity? Uhmm...interesting.
A 'real honeymoon' waiting to happen...lol