As far as I have seen on this forum nobody has stepped forward to be the pioneer to see this swap through to the finish line, a lot of talk but nobody has found a dealership willing to work with them on the tricky parts such as getting an 8.4 unit with the right VIN and options encoded into it (some claim they can't and maybe its true). I don't know about the 7" unit but the 8.4 contains all manner of climate control and user preferences, settings for this and that, controls for heated seats if you have them, and the NAV unit has SXM Guardian capabilities for which you need to add to your list a replacement rear-view mirror with the buttons and don't forget you probably need a different antenna and possibly wiring for that as well. Its going to be very difficult to accomplish and you are talking about the newest vehicles out there with the latest version of the uconnect system, very little information exists, very little time has been spent reverse engineering it, very few people even want to try once they find out what they are up against.
There are many posts in this forum like yours of people looking for info, they get some and learn about the difficulties they face, then their threads go dark and quiet.
If I didn't already have an 8.4 radio, and I was determined, my first step would be to make friends with the dealer service department guys and find out exactly what is and isn't possible for them. Because of VIN locking I don't think there is any way you can possibly do the swap without the help of a dealership, you are dead in the water right there until you have them on board if the radios are truly locked to their VIN.
First off, realize they have nothing to gain from helping you out. Its not a money-making opportunity for them. The entire service shop's only job is to turn those people's time into money, by doing oil changes and brake/tire service and writing up service orders. Probably FCA has provided no upgrade path on these radios, the corporate attitude is likely that they come with what they come with. Therefor, the dealer has no information from FCA on how to upgrade a radio and no standard way to go about it, probably very little support from FCA is available to them at all. (Hopefully that information ends up being incorrect but starting with the most likely assumptions) Because of that, the service department is stuck in-between you and FCA in a no-win scenario. The hours you are asking them to put in to cludge their way through an unsupported radio upgrade make it a huge money loss for them right up front. My advice would then be to ask as little of them as possible. Plan to do the hard work and the trial and error on your own, or hire a local aftermarket stereo shop for that part.
Tell the dealer you just want to know if they can order you an 8.4 radio paired to your VIN, with all the fixings (bezels, rear-view mirror, wiring, antennas, etc) and that you will take it elsewhere and try to make it work, at your own risk. They are not going to want to be responsible for it when it all goes south. This is the point where you will find out if the dealer is even able to request a different radio than the VIN specifies from FCA for your car, so this will be the sticking point. It all depends on how these radios are designed. The service department is probably not going to know enough about the radios to say one way or another, but if they are willing to at least ask FCA for an 8.4 tied to your VIN and they don't say no (at FCA) then you've got a chance. If corporate refuses to send an 8.4 radio for your VIN, you might be screwed. Here again, it all depends on what the dealership can and can't do.
Some people theorize the dealer has some magic "scanner" in their hands which can "program" a radio for a given VIN. I have never seen any evidence of the existence of such a device. I think it is much more probable that the dealer's only option is to request a radio from FCA with the correct VIN already programmed into it. This is something you have to get to the bottom of to complete your quest. This is why you need to be on really good terms with the service department. You need to know what the dealership can and can't do. The thing is, there is a LOT they can't do. They like to pretend they have full control over your vehicle, when the truth is other than un-bolting and bolting things back on when it comes to the electronics they barely get enough information from FCA to do anything, and they don't like to admit that, so its going to be tough to get the truth out of them.
The service department will be in a tough spot. If it is, as I am guessing, that they have to ask for FCA to ship a radio with VIN pairing already complete they are going to probably have a hard time asking for the one you want. The abbreviated conversation there is going to be like;
DEALER: Hey, can you send an 8.4 radio for VIN# 123XYZ?
FCA: Our records indicated VIN# 123XYZ has 7 inch radio, we can gladly send you a 7 inch radio for that.
DEALER: No, want the 8.4 radio.
FCA: Records show 7 inch for that vehicle...
All you can do is try and see if you can get that far. You have a wiring nightmare ahead of you probably after that but first someone has to see what the extent of VIN locking is on Uconnect systems and answer the question "Can you get one paired to a VIN that is different than what the car came with?"
If the answer is yes, you can move forward one step.
Researching in the renegade forums might be worthwhile since they are very similar but have been out a couple years longer. Be aware they have an older version of the Uconnect but the base technology and corresponding capabilities are probably still the same.
Best of luck, would be nice if one of these threads didn't go totally silent for once and have someone actually figure it out.