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A patent application (US 2008/0180565), which was recently published makes it clear that Canon are indeed working on a fuel cell DSLR. The fuel would act as a single source of power and here is an excerpt from the patent:
. . . an electronic equipment system in which fuel cells are provided to an electronic equipment body [ed., a DLSR body] and a connection device [ed., a hotshoe flash] connected to the electronic equipment body, and in which detection of a battery remaining amount and control of electric power supply can be performed under unified management [ed., one fuel cell], thereby enabling simplification of the electronic equipment system and improvement of power generation efficiency thereof. 
[Via Photography Bay]