I think the issue would be where to hide the end of a pull cord - so more than just saving the 1p of the cost of a pull cord, would also need to add an access door.
Checked my boot in my ST and it's just carpeted, I bet most Audi's have a little removable hatch/door which would be easy to hide a pull cord behind.
There is a vent which maybe ok to have a small pull cord come through, but it would be visible.
 
I don't recall the seat part even having the manual release option at all so assuming it physically fits you would still have to get the audi actuator and then go to the trouble of finding a way through / access hatch etc. 50 / 50 whether it fails open or closed, either way if mine fails again it's defo getting disconnected