Something along those lines seems to be in the works, from the International Tribune:
Benedict said as he arrived in Lorenzago on Monday that he hoped to start writing the second volume of his book "Jesus of Nazareth" while on vacation. He also said he would begin writing an encyclical, which Lombardi said would be on a "social theme." News reports have suggested it would cover issues of globalization.
"There is also this idea about an encyclical, which, however, still seems to be at a very early stage, at the level of reflection on how it can be laid out, even though the social themes" are at the heart of it," Lombardi told RAI television. "It is still not at the level of production, of actual writing."