at least one other member on the forum has done a 7 -> 8.4 swap. if you watch ebay you can probably get an 8.4 take out for way less than that site is charging for them. There are some... "side effects"... to doing the swap that you should know before you dive in. Check these threads:
1. I was aware of the Infotainment site. I found cheaper on ebay. Whoever you choose, the seller has to provide you a take out VIN/access code, or the seller has to have the capability of resetting to pre-new install-never-been-mated-to-vehicle. Otherwise you have a brick.
2. Basic swap is a no-brainer. Just plug-n-play.
3. Uconnect/Sirius Guardian will not work - without a lot of effort. That's not a show-stopper in most cases.
a) you will need to get an LTE antenna. See the threads above. And a cable.
b) you won't have the SOS/ASSIST AutoDim mirror. You can order the mirror, but the replacement jumper harness you need will not be available. This may or may not impact ability to enable Uconnect/XM Guardian. SOS/ASSIST can be operated from the screen.
c) FCA/Sirius "database" mates the radio to the ORIGINAL VIN, that requires a call to correct. Again, in the thread. This is the biggest hurdle to getting this working.
4. Registering regular Sirius XM is not a problem, there may be even an existing trial for XM/Travelink, depending on when your radio was originally activated.
5. You might be able to resell your 7" to Sport owners with the 5". You will recoup some of your money.
6. If the unit goes belly up, you are on your own. Updates may be problematic.