First, don't listen Pioneer and think you need to buy a special USB cable to get MirrorLink to work. You don't.
Second: I finally discovered why MirrorLink wasn't doing anything between the Note 4 and the 8000Nex when I would plug in the Note 4 and the phone would say it's connecting to the head unit via MirrorLink.....there's a whopping 1 app actually supports it...barely, and that app is Aupeo. With Aupeo installed and the 8000Nex set to Other phone and USB, it will activate MirrorLink and when you select the Apps mode on the 8000, Aupeo shows up as an icon without needing to run AppRadio, and selecting it brings up its radio UI. However, there's no audio. I've tried multiple mode changes and nothing appears to fix it, so there's no indication what's causing the lack of audio; the app, the phone, or the radio. At least this shows that if devs would add MirrorLink support to their apps they will work and would make up for the lack of Android Auto on the 2014 line, but there's no indication that's going to happen, especially if Android Auto uses a different means of piping apps to the car stereo.