That's a very good idea. I'd love it if cars had this.
...or just have device side usb port that shows up as a mass storage device?
That would be pretty inconvenient for appliances in places that are hard to reach with a computer, but definitely an improvement over the status quo.
I’d like to see them all have a USB port. If you plug in a thumb drive the appliance should create a directory named with the appliance manufacturer and model and serial number. In that directory it should place a copy of its manual and other documents that normally come with it.