I only did some code mirroring and administrative stuff. All the work here has been done by @jnsp, thank him, not me,
@jnsp: oops, I’m late. I could have saved you some search time with that. I inspected Keyguard sources few days ago.
Android 5+ don’t support lockscreen widgets anymore (unlike KiKat did). The only way to achieve that behaviour would be coding an alternative lockscreen with the widget embedded, although that sounds a little error-prone.
Backporting the lockscreen widget functionality to the regular Clock Widget seems the first thing to do, anyway. Skipping the Fairphone-specific part doesn’t sound to be extremely difficult (check the phone model), but there’s in fact work with the battery stats.