Unions had been given until Friday to join a due diligence process that allows a more thorough examination of the concept and the massive financials involved.
Signing up to that wouldn't mean a commitment to joining the Nations Championship, a 12-nation inter-hemisphere extravaganza set for 2022 basically involving the Six Nations teams and an expanded Rugby Championship taking in Fiji and Japan.
World Rugby are proposing two divisions below that with promotion-relegation play-offs coming into action to keep teams hungry.
The relegation threat and the financial consequences are a real sticking point with the Six Nations who have enjoyed a cosy and profitable existence for so long without having an fears of losing their place in Europe's premier tournament.
The Guardian reported the week's grace to allow unions to further consider the proposed format and it's impact in what will be the game's biggest shakeup since it went professional for the 1996 season.
New Zealand and the Sanzaar nations appear keen on the idea though deny the problems of getting agreement are as simple as a north-south split.
"The reality is that we have a great idea but it comes with complications that need analysis," NZ Rugby chief executive Steve Tew said.