Hi, Yes the LIN-Bus is 12 V but if you could use the oscilloscope inputs which is ±25V to do the analysis there should be no problem.
Another manufacturer of USB oscilloscopes "Picoscope" has this functionality (and a lot of other serial interface decoding support) already, so why can't you add it?
As I tend to use the Discovery 3 more and more and I do not like to carry around the bigger Picoscope in my backpack when I need to go faultfinding in vehicles, the serial interface decoding option with multibus combability is really a thing I would like you to add.