I too am very sceptical about it. Writing a policy doesn't mean it's going to be happening. OP should know that if he works in the APS.
Correct, cost of administering it overweighs the revenue. The intergrated cargo system ( the program that CBP uses to administer tariffs and taxes) is pushed to the limit already, is hard to use, and antiquated. It does, however, work.
Now, how and who pays?
How do you tax the mail/postal system, that doesn't use ICS?
Where do you store 1000s of tons of goods that haven't been paid for yet? I know fedex, ups, dhl sure don't have the facilities to store them. Space on wharves are at a premium, and CBP doesn't own any warehouses.