They had something called the Australian Provincial Championship (APC) before they introduced the ARC in 2007. It was all the Australian Super 14 teams playing in a tournament after Super Rugby had finished. I think they only did it for one year.
As others have said, I wonder if something like that would be a good replacement for the current NRC: have the Australian Super Rugby teams + teams from GRR playing in a tournament after Super Rugby and GRR finish.
It would still tick the box for player development as all the test players would be out for most of the tournament. And there could be other potential advantages as well:
1. Club players might have more of an interest in stepping up because they would get to be directly involved with the Super Rugby teams and coaches, etc. The step to professionalism might seem a little more reachable: club to Super Rugby team, rather than club to NRC to Super Rugby.
2. It might even develop players better than the NRC does. Smaller pool of players, more competitive teams.
3. The Super Rugby and GRR teams benefit as they get more of a chance to develop and build for the following year: coaches get to directly control the trialing of new players and combinations in their existing structures, they can also build on existing combinations, and the teams can bring in a little more revenue to account for a shorter Super Rugby season from 2020 onwards.
4. It might be a little more popular than the current NRC since the tournament would be using more familure brand names. And in a sense, the Force get to come to the party again with the other Super Rugby teams.
5. SS clubs might be more accepting of the idea (or might be less able to resist the idea even if they wanted to). Clubs are perceived to be the third tier again directly beneath Super Rugby (and GRR).
6. This tournament might be better for test players to play in when they are out of the Wallabies and/or returning to form.
7. other ?
Downsides might include:
1. Fewer club players would be asked to step up to the next level as there would be fewer spots available.
2. Club rugby may have to rejig how their season runs.
3. other ?