I just pulled out all the rear carpet/sound deadening and rear seats, saves around 60lbs (weighed on scale) and I see this which i've never seen on other 4's before, im quite sure its original, the threaded mounts are clearly a factory installed piece)

 

heres a pic of the mount and also the roll of trunk liner I bought, looks soooooo much better than the crappy original carpet.

 

i think the thread inserts are for the gas tank straps?

maybe those things in the first picture are for a carseat?