What you've said is true, but it's irrelevant.
content_revision and
image were merely the objects you gave in your example. What if your new object inherited from
user or
group or
apm_package (not so strange, actually...)?
In fact, of the many things within CR/CMS to be fixed, this isn't one of them. CMS contains (and will contain) pages which accept object_id's and perform actions upon them. An object_id is a revision_id is an image_id is a wp_image_attachment_id. The same ID number appears in many tables which belong to many packages.
There are cases where you want to treat acs objects as atomic, but as it stands, for the purpose of permissions, they aren't.
