Re: 2014 8.4 using iTunes on SD card?
Itunes supports a number of formats that are not compatible with the UConnect system. For example MP4 is Mpeg4 which is a Video Streaming format which I am not sure it can play. Also there are a lot of AAC files often in itunes which likely also wont play.
You can plug an ipod directly into the USB interface or if you have an Apple phone you can also play wirelessly via Bluetooth (iPads too)
If you have an Android Smart phone and want to sync with iTunes, get "Sync Tunes". Allows you to wirelessly keep your Android phone up to date with your itunes library and it plays seemlessly with the Jeep in Bluetooth. (Still no Album art on Bluetooth but I assume it is coming as it works in my 2011 Durango no Problem).
I have tested the above on the 2014 Jeep, let me know if you have any questions.
Though the SD card is a nice idea, it lacks the stored Playlists etc that you can do through another device. Had the SD Card in my Benz, stopped futzing around with trying to work with it after a few months.