I had an 8000 NEX installed in my 2014 Outback, and just got my car back yesterday. The installer and I spent a few hours wrestling with app mode. We initially had trouble with the cable - iPhones are notoriously picky if you use non-Apple cables, which pretty much rules out the use of an extension cable. They hid the lightning AV adapter (necessary for app mode) inside the dash, and used a lightning extension cable to come out of the dash into the phone dock. Looked good, but didn't work.
Once we got the cable issue sorted out, App Mode was still incredibly rough. You hit the app mode button, wait maybe 10 seconds for AppRadio to get going, hit the "allow" button, and eventually your app icons are up. Hit the music icon (I forget the exact name), and wait another 10 seconds for the CarMediaPlay app to come up on the phone. If you switch over to map view on the 8000 and the phone leaves the CarMediaPlay app, then if you want to browse music again we almost always had to force quit CarMediaPlay before we could get back into the music browser again. It was very, very painful.
In the end, I cried Uncle and asked them to connect the dock directly to a USB input with a stock lightning cable. No fuss, and everything just works. Music plays right away, without waiting for apps to boot up, and no force quitting. I don't have app mode, and I don't have any video, but I like the built-in non-app music browsing interface on the 8000 so I'm mostly happy with it.
I asked the installer to leave the HDMI cable connected and poking out of the dash, so I'll try app mode from time to time, especially after firmware updates have been released. Of course I will try out CarPlay once it's available. My better instinct tells me to wait 2-4 months after release before I try it, but I'll be lucky if I can hold out 2-4 days.