It's a great question!  I think for 90% of plugins out there, swapping `sbt.Plugin` for `sbt.AutoImport` "just works".   For some this may be all that's needed.  It promotes the idea that the notion of plugin we have today is actually "library of Setting sequences".

I think migrating to true plugins (with auto-addition and dependency management/inclusion controls) will happen with time.  I'll provide a migration guide to this effect for the 0.13.2-RC1.

I think this means, we'll cut an M3 now.