I agree with Dave.  We may put package_id into acs_objects as early as 5.0 depending on how much other stuff we take on (we need to finish 5.0 by mid-summer because a couple of universities are heavily invested in seeing .LRN 2.0 work by fall.)

Upgrade scripts to copy package-specific datamodel package_id columns into an acs_object package_id column will be very easy to write, PG now has DROP COLUMN so that will work, too, and hacking the relevant queries will be easy enough.