It's a very big deal, though I think unlikely to actually happen (unless the RSA official sporting world implodes on rugby, as it threatens to do). At least three SA franchises (Stormers, Sharks, Bulls) are top-half contenders, which year-in and year-out is about the same as the K1s or Aussies can manage. Super 12/14 annually tees up Tri-Nations. And, in addition to the hugely expensive NH-RSA airfares, the seasons are wrong.
More importantly, there are long ties of competitive rugby between RSA and NZ/AUS, and logistically it continues to make sense. The level of competition provided by the PI teams is nothing like that available in SA, and (other than their national side), that's true for Argentina, too [most of their Test players play club rugby in FRA or ENG, not at home]. NZ and AUS can't come up with 5 additional competitive teams to take the place of the SA franchises (look at the financial problems with the ANZ expansion, and splitting any of the current NZ franchises would seriously weaken them competitively), and the TV revenue for dropping back to 9 teams would be a killer.
This idea makes very little sense.