I have exchanged email with A PADI Official about the Scuba Merit Badge. Few specifics are available. The BSA has approved the development of the badge. PADI hopes to fast track the actual badge and would like to see it in application in a couple of months.
The Merit Badge is going to be much more involved the the BSA Scuba Award. The suggestion being put out to dive shops/operators is to use the BSA Scuba as a teaser/intro into Scuba. If the Scouts like SCUBA, then they can sign up for the merit badge with the dive operator.
All of this could change of course. This is what the PADI marketing is seeing as the relation between the two awards. Initially, I interpreted this as the MB involving something similar to a CERT, but I could be reading more into it than what is there because certifications do cost money.