Well, I'm going to add to this thread...I just discovered that, apparently, my 2013 Prestige A6 does indeed have the rear lid foot sensor as found in some A8's. If I stick my foot under the rear bumper twice (and the advanced key is in my pocket) the trunk will auto open.
Scared the heck out of my wife when it unexpectedly happened.
There's nothing in the manual about this so I expect it was added afterward, possibly only for MY2013. It definitely has it's advantages if your hands are full and you want in to the trunk.

Does anyone with a 2012 have this feature and has anyone with a new 2013 discovered this?

Holy freaking crap! That's awesome! Mine does it too! Its in the manual (at least mine) towards the front of it. It's not mentioned anywhere in the window sticker, US website or anything. Nice find! Wonder what else the car has that wasn't mentioned... Hmmmm...

Where in your manual? On Page 37 in the Rear Lid section, mine makes no mention of it anywhere.

Does it unlock only or actually open up the trunk lid? Do you have the auto close button on the inside of the lid next to the locking mechanism? Can you open and close the trunk using the driver side door button?

Yes, the lid unlocks and opens. Not powered but via spring so no auto close button.
Yes, the lid can be opened via the front door switch or the key button.
And two waves of your foot under the bumper.

Whacked shin!
 

Tried it on my 2012 Prestige. Did not work, so tried more vigorously bruising my shin on the bumper, to no avail!

My wife is having a good laugh.....

Yeah I'm seeing the same thing on my 2012 Prestige. I got some strange looks from my wife as I was trying to test this out today lol.

Nice deal for the 2013 people. Wish we had it on the 2012.

Time for a survey....
2013 Prestige/Innovation. No dice with the trunk open with strategically placed foot.
I tried waving my foot under the bumper a few times. Tried side to side, back to front. A few times each. Saved my shin, though... ;)

I'll try again whilst carrying a couple packages. Maybe it knows....

FWIW, it works for me if I stick my foot under the bumper once, pause and stick it under a second time. Waving the foot side to side does not seem to work. Key fob must be in the immediate vicinity. My wife tried it with her key in her purse and it also worked for her.

Page 40 I think. Took the picture with my phone but had to get into work and forgot the number. Its below the 100s in the page numbers. Here is a picture of he manual.