Okay, I've reviewed this a bit.
I don't see any reason to force the creation of id-only extension tables on people who only want the other stuff that acs-objects provide (audit data, permissionability). We need to de-cruftify.
To repeat what's probably an assumption, as part of this TIP you'll have to grep through and fix any code that expects non null values here. I found the acs_object_types table popping up quite a bit in the acs-subsite/admin pages, something you didn't mention.
Also, while you're at it, you almost certainly want to drop the not null constraint on id_column, and probably on package_name as well.
Bottom line: APPROVE
