I actually had the same issue in my 2011 Chevrolet Camaro, I was using AOKP rom and Franco kernel with Fast Charge, I had to disable Fast Charge within the kernel itself because of issues I was having with USB on the computer, to make a long story short, I decided to see if my USB jack in my Camaro would recognize it, to my delight, it did after I disabled Fast Charge. It started indexing and shortly after it let me access it like it was an iPod, including playlists, artists, songs, albums. It loaded up the name of the phone and used a weird mode called PFD (PlaysForSure Devices (PFD), I never saw it before, and I tried looking online to see if others had the same thing happen to them but apparently no one has tried. The Camaro has a pretty powerful radio since its one of the only cars to support ZUNE natively like an iPod
In my opinion it works more efficiently than MTP and Mass Storage, I like it better than my iPod lol I just wish I could get my playlists to work, but I read somewhere that the radio only can play up to a max of 166 songs per playlist or it won't recognize it.
My main reason for being happy about this is because I get to see my song info on my windshield HUD when it goes to a new song, with bluetooth i don't get that option since apparently it doesn't support AVRCP 1.3 (only 1.0
Those are my findings so far. I think Google made a good choice by going to MTP because if its used right, all Android 4.x devices could work like iPods in the future. (one reason why people still want an iPhone over Android devices, atleast my guess anyway, convenience)