Every cr_item eventually has a root parent_id of either -4 (security_context_root) or some other non-cr_item.
So we can just find the item in the hierarchy that has the non-cr_item as the parent, grab the parent_id referring to the non-cr_item, and select package_id from that acs_object.
This query seems to work
select acs_object__package_id(parent_id)
from cr_items
where tree_sortkey=(select tree_ancestor_key(tree_sortkey,2)
from cr_items where item_id=new__item_id);
I can replace the call to content_item__get_root_folder in content_item__new with this.
