With regard to Adelaide not being viable for a team base there, why not take the AFL model where one of the established teams regularly plays some matches there - say it was the Stars, and get them to play 2 home matches in Adelaide each season, as the AFL does in Tasmania (and used to do on the Gold Coast until the GC Suns were introduced) to build up the support.
They could work with the local rugby community - hold training sessions for kids and emerging players etc, get media attention. I know that the Tasmanian Govt sponsors the AFL team that goes there (not sure which one it is) because it develops tourism, and it caters to the local AFL fans there who probably buy team merchandise etc.
I think that this would be a way to build the support without the overall cost of putting a team there when the infrastructure isn't developed enough. Yes there would be costs to the ARU for the travel of the teams to get there but this is part of growing the game. While the Rising might be more close geographically to Adelaide I think they need to keep working on growing the support in Victoria, and since the NSW teams are struggling for support, get one of them to take a couple of games - might get a bigger crowd than the Stars did at home. Possibly Sydney Uni has some links to Adelaide Uni so could tie this in as well.
) so the Brumbies are going to boot the Red and Whites into touch.
