There's no way automate it with the current hub architecture and today's technology. You'd literally have to have a stadium-sized package 'cache' where all package could be unloaded to, some machine vision doohickey to characterize every package, then have a solver identify the idealized load configuration, then picker bots go out and start streaming packages in order so that some high end robot could load the trailer with 90+ percent packing efficiency (which i believe we achieved as loaders getting paid $8/hr).
Then you'd still have to leave the last 8' of trailer space to handle the goats heads and exhaust pipes and all the other crazy shit that people just slap a label on and make someone else's problem. Maybe you could find a way to use air bladders or some kind of encapsulating foam to handle that, but mostly you'd just have to have a floater running from trailer to trailer to load that stuff.
(internet fist bump btw)
It is too complicated to design a system that handles 100% of cases, better aim for like 90% with well integrated fallback for the edgecases.
There is a lot of idiosyncrasies like this with many of UPS' jobs. Automation will come not to take the paycheck from the low wage worker, but rather from the high wage worker such as driver dispatching, human resources, etc. Those people won't be fired though, most will be reassigned to over see some drivers I would imagine. That is a tough job and those people need all the help they can get.