I've been talking about an idea like that for ages....
Top 3 teams (or whatever number) from the national leagues, gets together for a month at a point in the year and duke it out to find a winner.... would be a great way to rebuild local rugby structures to a degree and have a great competition for everyone to watch after the fact.
Think about it, it would make Currie Cup an even better series to watch... and then we'd have a short but intense "World Super Rugby" league that had none of the jet lag, travel etc bollocks.