I have done something I can't show you pics but i can explain the whole idea. I have been testing it for the last 2 years and the more i use it the more i discover hidden functions i didn't know about.

What is it?
It's a combo 2 cases + attach systems
Where ?
On the rear rack
It can be adapted to virtually any standard frame bike on the market, cargo bike as well

Functions of the cases + attach systems:
-professional looking
-carry more than 50kg with some cautious measures
-weight around 3kg
-it costs me around 80$ in total
-cases carry more volume than most backpacks on the market
-cases are attached in less than 30s (2 redundant attach systems)
-other items are attached in less than a minute
-cases can also be carried on the shoulders or by hand
-the attach systems can carry 2 backpacks
-a standard groceries bag can securely be attached to the system in less than a second (not a joke)

-With the attach systems I have easily attached and carried on my standard bike:
---a 6 feet long floor lamp
---a wooden chair
---big boxes, small boxes
---a small table
---monthly groceries (more than 100kg)
---suits

-adaptive shape
---accept from 2 to around 20 rear lights + reflective tape + signal lights
---adapt the height of the rear lights for more visibility
---carry from a small box to 2 6-feet-long lamps
---up to 4 suits with hanger for white collar or 4 wet clothes to dry on the road for touring
---a special compartment for up to 2 sleeping bags and mats easily attached

-security
---cases are secured by codes
---cases are easily attached to the bike for temporary absence
---cases are water and shock resistant
---reflective tapes can be added on the cases for lateral and rear visibility

By the way,
the tour milk crate from the link isn't secured because its center of gravity is way too high. Because of that it can accept only light items