So, I spoke with a rep and his supervisor in the parts department at the dealership. I explained that Stage 1 and 2 were something I definitely wanted to do in 2020, among other things, and I was doing my research now but there were issues. The 2018 model year was indeed grayed out for stage 1 in their system. When I pointed out the Cat-back exhaust's status changing from the previous year, they did find that to be weird. Their thoughts were that the Chrysler engineers didn't like something and didn't want dealerships installing anything without consulting them first. We had to submit a request to Chrysler with my VIN attached before we could go any further. After about 30 minutes to an hour, a response came back with a part number for the 2017 Scat Pack Stage 1.
The rep said in the future, if nothing changed between the 2019 and 2020 catalog, this would be my best option but admitted that he wasn't sure if the request would be fulfilled. I believe he said they tried something similar in the past and the order wasn't fulfilled. Good enough for now I guess.
When I got home, I checked the part number but it didn't match anything in the 2018 or 2019 performance catalogs. I googled the number and got a match on a Mopar Parts distributor site. The part number was indeed for a 2017 scat pack stage 1 but it was out of stock and while it had the cat-back exhaust, it didn't have the cold air intake, which made sense. The cold air intake was not available for for the 2017 and up models in the 2018 catalog but it is available for the later years in the 2019 catalog. The Idea would be to install that 2017 scat pack and then install the cold air intake and go from there.
So, it looks like for now, it's case by case if you want to install Scat pack stages on 2018 and presumably 2019 RTs. Good luck to you and everyone else thats trying to install Stage 1 on a 2018 and 2019 models this year. I'm hoping for good news in the 2020 catalog.
Also, you can order Stage 2 and stage 3 tuned PCMs from Mopar parts distributors including Prefix