Hi NNN and Manuel Jander! After some trial and error it seems I was able to fork and compile libwbus partially on a Raspberry Pi and get wbtool working with a K2L901 USB OBD KKL cable in my car. I built the adapter cable from the OBD connector to Webasto Telestart connector by myself. I also have the is0-mick 2015 / mickr1969 fork of this running on a Arduino Mega with a DIY adapter based on the L9637 chip but for some reason the Arduino fork isn't reliable enough for daily use (lot's of random timeouts...
libwbus for Rasbpian, wbtool working partially and wbsim compiles on Rasbian Stretch lite