If you do a side by side comparison on the Pioneer site you will see that the units are "feature" identical except when it comes to the screens and Android Auto support. This of course doesnt mean they are "chip identical" but someone else has already tore apart the 4000 and 4100 to reveal they are pretty much the same device sans screen. That doesnt mean the 8000 and 8100 are, but it is suspected to be as well. The Android Auto difference must have been in the screen, but we can see that it works anyway using the hacked x100 software on a x000 unit (even though bluetooth isnt currently working). So more than likely, this is something that could be implemented on our x000 devices with a general disclaimer of "it may not work as well as the x100 that was designed specifically to Googles specs".
Pioneer more than likely will never do that. Even though I would gladly pay say... $100 or so to update to the new "features" of the x100 platform. Note that I am not wanting to pay for "features" that I have already paid for and STILL EXPECT TO GET *cough AVICSYNC cough*. They really could learn from the phone manufacturers who send out free updates across several generations of devices, with each getting a little slower, but still having general functionality of the newer devices. Eventually we would all ditch our x000 devices for the x400 device because it was so much quicker than our devices.
Or just go open source and let us customize our own devices like we used to do with the AVIC700/900 series.