Out of that list, only Roos has a shot to be included before RWC2023. And Roos and Louw need all the URC experience they can get. They can be called into the Bok camp during summer 2022 and still feature during the RWC.
I don't see Thor being included in the RWC2023 squad unless it's as a veteran presence. He will be 37 by that time and I think his move to Ulster was a passing of the torch to Louw ascending to the #8 jersey.
If Thor is not a factor, then you have 8 jersey and two more loose forwards up for grabs. Weise, Kwagga, Van Staden all have gotten cracks. But honestly, I could see all three not making the RWC2023 side for different reasons. If I was a betting man, Kwagga would be my top choice of those three because of his versatility and fetching ability. A big knock on all three is their height and inability to be a lineout option. That's why Louw at 6'5" and Roos at 6'4" must be appealing to the Bok coaching staff.
If we go with 5 loose forwards and everyone is fit, I expect it to be:
6 - Siya
7 - PSDT
8 - Louw/Roos
21 - Kwagga