As Nige was apt to say, this is not Soccer.
Cup competitions work well in football, where you can expect, that with a bit of luck, a well coordinated and physical side can prevent the opposition from scoring, either at all of more than one, despite being inferior financially, or skillfully or managerially.
A Tasmanian team for example, would likely have the metaphorical snowballs chance of beating say Box Hill, let alone playing Randwick, Sydney Uni or Norths. That contest does sweet fanny adams for anybody, regardless of level.
Then there's alignment issues. Who does Jordy Reid play for, Manly or Melbourne? How about Caydern Neville? How stacked does Sydney Uni get, and suddenly we've got another psuedo Super Side? Or are player points in effect, and some boys who need to be playing rugby are left unable to play?
What of players like Alex Toolis or Billy Meakes? They've come home from playing overseas and have started playing NRC. But in a club competition, who would they play for? Late season signings seem frowned upon at the best of times, let alone for a specific new comp.
If the NRC needs to go, it will go in 2020. A club comp, and particularly a knock out one, is not a suitable substitute. Should SANZAAR go belly up, some sort of National Comp mashing together the Super Sides, NRC sides and Clubs may be the solution, but until then, I think it's the NRC or nothing.