I believe that most - or even all - of those adapters are just standard OBD-II devices with either a bluetooth link or like the moj.io and Telekom ones to have a GPS tracker and mobile network HW and a SIM card included.
If it’s just about location tracking, you could put an old smartphone into the car and use owntracks.
If you want to obtain car data, too, you might rather like to go for a generic solution to work without moj.io. I would not expect them or any other company to support an open API in the long run.
Have a look at this old thread and the links in there. Maybe you could get your developer to use that as a basis for your next-gen solution (it would rather be an app than a binding, upstreaming the data using MQTT) to work on a generic level (i.e. it’s supposed to work with any of those OBD-II devices). And if you then were willing to even share it with the openHAB community, that I would be a great gift.