there is a cost to the end user for the use of the amazon interface.
the developer would provide a jar file that locks the code to his payment system.
so open sourcing the Amazon interface probably won't happen, in ofbiz.
you can however get java code (with apache 2 license) to work from http://developer.amazonwebservices.com/connect/
and get support from http://www.amazonsellercommunity.com/forums/category.jspa?categoryID=4