WR have also suggested a potential parachute payment to any relegated union.
Those potential financial windfalls, so desired by struggling Southern Hemisphere nations, haven't been enough to sway England, who believe relegation would bring huge losses in ticketing, hospitality and sponsorship.
With the Six Nations needing to vote unanimously to alter their competition in any form, World Rugby's attempts to pressure and persuade the north appear to be falling on deaf ears.
"For us it could be catastrophic being relegated, commercially," Melville said at Twickenham today. "To be relegated, the catastrophe isn't just the team being relegated, it's our ability to fund the game as a governing body in England.
"In order to make it work Six Nations-wise, you need a credible tier two tournament. I don't know what you'd be relegated into at the moment. That tier two tournament is something we've got to build, World Rugby has a responsibility to build that because that's critical and having worked for tier twos I know how hard it is to do that."
Asked about the extreme suggestion that, in the unlikely event of relegation, England would be forced to sell Twickenham, their cash cow, Melville went further with his opposition.
"I think we make sure it doesn't arise. That solves that problem.
"You just don't want to get into a situation where you're making decisions like that. You've got to look at it as an opportunity to have a global competition, how can you get there, how quickly can you get there, what are the key points to get there."
Melville initially praised the "narrative" of the Nations Championship, only to rattle off a host of concerns that, given the timeframes, appear likely to kill off the concept for the foreseeable future. He later questioned whether the proposal would undermine the Six Nations identity.
England's apparent objections centre on clashes with the European club season; player welfare concerns due to the potential of teams from the north having to travel to three different countries in the July window, and the prospect of languishing in a tier two competition for at least two years, with the Nations Championship not being contested when the Lions tour or in World Cup years.
"It's not quite up and down, one season on the naughty step and go back up, it's actually two years and that could be a disaster for people. But a credible tier two, when you've got a buoyant competition, you can see that working."
In something of an about-face, given the refusal of the Six Nations to open its competition, Melville questioned whether the Nations Championship held the best interests of tier two at heart.
"Tier twos no longer get tier one games. So how does that help them develop? Because the previous model was give them more tier one games, and commercially that's good when you're at home, to bring them up to speed for a World Cup.
"This changes that model into just tier twos versus tier twos and then go to a World Cup. Does that make them more competitive? I don't know but that's an interesting one."
Read between the lines and it will take an almighty backflip for the Six Nations to support the Nations Championship concept with any form of relegation attached.
If agreement is not reached in the next two weeks, World Rugby risks losing the investment tabled by Infront, and the whole concept may then fall over.
"Two weeks for a 12-year decision…. it's not easy but we've just got to talk it through. The board are meeting tomorrow, we're meeting tonight. We'll look at it and respond accordingly. But it's not just about making a two-week decision, it's looking at the options and getting those on the table and keeping the thing moving forward, take a look at it in a bit more detail and answer the questions that are all being raised."
