So, seems like Dead Rising 3 is (edit: possibly) official.
Yay!!!!
"Being careful not to confirm any story details, Capcom COO David Reeves told CVG that more digital releases are almost a dead cert - and will "bridge a link" between Case Zero and Dead Rising 3.
"Obviously, with all of that success on Dead Rising 2, it makes sense to move onto Dead Rising 3," said Reeves. "I think that they [developer Blue Castle Games] may extend it by bringing in new characters and new interactions, or bring back others from before." --Taken from here
Also good to know - DR2 has sold over 4 million copies in less than two months. GREAT SUCCESS.