There is a "package build under the covers" document available on the Oracle support website. When you log on, search for "E1 PKG Under Covers". If you are asking about changes to the actual "process" of assembling, building, and deploying a package...not much change other than in 8.12 the current full package takes on a bigger role and the system notes the currently deployed full. But the process of assembling, building, and deploying is essentially the same.