Re: A paranoid mount option ?
"Maybe someone could dream that up with a Raspberry Pi ?"
I was just thinking of doing this with an Arduino. No need for the RPi's power.
My solution was to create a device about the size and length of an adults thumb that allows you to plug a USB A device into it. It would then tell you how that device was presenting itself to the host. You would be able to see that a flash drive is presenting as a flash drive and as a HID device at the same time.
If it is a USB keyboard I was going to have this device try to capture any keystrokes. You can use it to test a real keyboard or see what a flash drive is trying to type into your shell if it appears as a keyboard.
I was also thinking of having an option to wipe out the partition table of the flash drive so to reformat it you need not plug it into a computer at first, putting that machine at risk should it do something silly and generate thumbnails for images on the drive when you accidentally open it instead of right clicking ;)
It could also let you confirm that other USB devices seem to be working, so you can check that second hand PS4 controller seems to be trying to connect and has an unbroken cable.
Using a RPi would allow you to do many more things such as check the files on the drive etc.
Thinking about it, an RPi zero would fit the form factor I'm thinking of.