Hi Leo,
thanks for your note and offer of contributing an xAPI tracking plug-in!
xAPI tracking is something quite high on our agenda, although, as Chris says we're not currently actively developing it. We would be very keen to work with you on this feature and support you with regards to how best to implement it.
I will reach out to you via email and see if we can have a call over the next few days.
Best regards and hopefully speak to you soon,
Sven