Hello,
just wanted to share my experience with Android Auto on AVIC-F970DAB (european version of 5100NEX)::
I purchased the Android Auto "license" by asd255 from eBay and everything worked like a charm. The procedure is very easy, asd255 sent me some files to copy on a usb device. Had to run 2 different scripts, first is to collect information from the headunit, second is to activate Android Auto. Doable for everyone who is familiar with personal computers.
I have to say thank you very much indeed, asd255, and can only encourage other people to give it a try, too! About 27 euros