Must be some sort of change to the swing arm on the 2018 RT. The previous trailer hitch is listed for 2010 - 2017 and a new part # for the one for 2018.
Electronics options are apparently different. The XM satellite receiver, the BT dongle, the CB communication system, and the cell phone interface kit, are all now listed as being for 2010-2017 with none shown for 2018. Maybe the CB and XM are coming later in an altogether different configuration because of the new cluster. The BT dongle and cell phone aren't needed for 2018, I don't think, as the new cluster has BT connectivity.
GPS accessories are still listed for all years RT so I take that to mean an external GPS can be added on the 2018 even though there is one in the the new cluster.