I'll start with the obvious one: we really need the 'Sequential or H-pattern' and 'Sequential or H-pattern + clutch' options from DR1. edit: this was added in patch 1.6, good job 🙂
Beyond that, I definitely like the way multiple input devices are handled, it's a big improvement over DR1 and makes it much easier to configure my wheel, pedals, gamepad and separate shifter independently. And massive props for the PDF document, it's amazing and super useful/interesting.
Another thing we were discussing on Discord recently is the Clutch Override assist. Why is this considered an Assist? The R5 cars, for example, have actual clutch pedals, and yet when the game is set to Sequential shifting, my clutch pedal doesn't do anything with the assist set to Off. Maybe we need a Sequential + Clutch option?
edit: another thing I thought of is that it would be good to include high-end wheels in the config by default, in particular the various direct drive wheels. I've seen a couple of times now for example Jimmy Broadbent streaming DR2 after a patch and having to edit the input XML file each time, to much frustration. It's a fairly minor thing but it'd go a long way to creating positive impressions.