Hello again,
Here is a small update after some days playing with the setup.
Armbian was moved to its Ubuntu flavor, where Panfrost is already installed so there is GPU acceleration.
Wifi stopped working after updating, but the (temporary) solution was to hold the firmware package: sudo apt-mark hold armbian-firmware
Sound interfaces are detected correctly, still pulseaudio defaults to the analogue output so one need to switch to hdmi each time the laptop is powered up. For the speaker initialization one has to copy the ptcommon module in the python3 folders, then modify the initialization script to pick up i2c-2 instead of i2c-1, and fire it at startup from rc.local. Volume control from the keyboard works out of the box.
Poweroff was also just a matter of changing the i2c bus in the poweroff script and install the systemd service.
What’s left for the moment is the battery monitor. The pthub2 module is not working for any reason, but ripping out the code to read the battery state from the hub registers works. Anyway a plugin for xfce would need to be developed to display the battery status, which is a bit cumbersome. Maybe displaying it on the desktop with conky is simpler, this needs a bit of thinking. Of course a kernel driver would be the best as it would allow to reuse the existing battery plugin…
Last point so far, switching the cpu scheduler from ondemand to conservative helped to lower the overall heating.
The RK3399 pi-top is quite an enjoyable experience now