Audio-Input (line level) and Retina MBP?

I don't think it is going to be possible. Look at this thread here:
http://att.macrumors.com/showthread.php?t=1390402

I just don't think I get why they'd remove it. I understand some will say you're not serious if you think you're going to record using that line in, but to take it away seems silly.

Also, from that thread you can get an adapter:
http://www.bhphotovideo.com/c/product/616367-REG/Behringer_UCA222_UCA222_USB_1_1.html

I use an interface very similar to this and I would need that adapter I think if I owned the MBP that didn't have line in.
http://www.bhphotovideo.com/c/produ...er_Q802USB_Xenyx_Q802USB_Premium_8_Input.html

 

The Sound Preferences pane has an option to select if you want to use the audio port for input or output on the 13". I can't imagine for a second they'd make it less capable on the retina version. I'm very sure you'll be able to use any 3.5mm jack input mic.