The motivation for this change is best described by @acorncom:

The goal here is to dog food the approach, find snags early prior to it being common and help pave the path for the community. Because although not having jQuery in your app isn’t ever going to be required, it’s the type of thing that would be nice to first allow (and down the road might become the new default blueprint at some point in the future). Plus, we’ll want to point folks interested in doing this type of change toward learning team apps.

For more info see the conversation on #38