Thank you, anon who dropped FinalIK here one day quite a bit ago. Good stuff.
[spoiler]only using arms IK though, seems like rest of body works really good just with ordinary unity joints and cheap trick of recalculating chest as weighted average of head and hip. Legs work flawlessly for example, they just wobble a tiny bit more when trackers are badly secured, but even that can probably be adjusted with physics[/spoiler]