Haven't had a chance to test it yet but have been looking through your code a bit. I doubt the others would want to incorporate a userland fix for stylus pressure but you should submit a PR with your fix for #317.
Hmm. Well, I really don't have any other suggestions. This is the first time I've encountered this kind of problem. If you figure out a solution be sure to post it. In general, a deadband like this is a hardware problem of some sort, be it the ribbon connector or the actual digitizer.
You say "was" working. Did you just check it in Windows? There's no reason to have the problem other than hardware failure that I can think of if you are using recent builds of VoodooI2C / VoodooI2CHID.
The volume keys are an easy fix, you just need to dump your SSDTs, find the volume key method and figure out what has changed. I'm afraid I can't add your device id, I am concerned that there's a small possibility of bricking your touchpad. The kext communicates with internal registers and I...