@ChrisVT are you still working on this? I'm currently running Ubuntu MATE 18.04 LTS on my HP tc4400. Some things don't work, but the wacom stylus does work out of the box. It won't rotate with the screen unless you change the settings with a bash script or manually (in the terminal), and none of the soft buttons work. They are recognized as hardware, but I haven't been able to get them working. I found an old article in the Ubuntu forums that someone patched the driver back in Ubuntu 10.10, but it was a manual patch for you to install that would get them working again.
The keyboard also has issues. Then I close the lid with the screen up (tablet mode) the keyboard is disconnected. That's all well and dandy. When I open it back up, it stays disconnected and now I cannot enter my password, so I have to restart the computer.
I also think that I need to test the keys on the keyboard to ensure that they are all doing what they are supposed to do. Some of it may be software settings, though.