World Rugby's revolutionary Nations Championship concept faces a crucial 24 hours as the powerbrokers of the world game meet in Dublin on Wednesday.
The Six Nations unions last month agreed to a period of due diligence while also weighing up offers from private equity.
Sources say there has been "real engagement" over the world league plan, and remain optimistic.
The deadline for a final decision is likely to be set for June.
Scheduled to launch in 2022, the Nations Championship would see a top division of 12 teams from both hemispheres play each other once in a calendar year, either through traditional competitions like the Six Nations or an enlarged Rugby Championship, or in summer or autumn Test windows.
The top two teams would then meet in an end-of-year showpiece final.
It is designed to globalise the calendar and increase competitiveness, with many international games currently glorified 'friendlies'.
A major sticking point is the concept - and the timing - of promotion and relegation, with certain unions keen on a period of ring-fencing in order to establish a vibrant and sustainable second tier.
The process of two countries joining the Six Nations and Rugby Championship sides in the top tier is also up for debate, with a 10-team first division being touted for an initial period before expansion.
Potential tweaks to the proposals will also be discussed at the World Rugby council meeting.
The players' union are also believed to harbour reservations over the travel required in the July international window, when northern hemisphere teams traditionally play in the south.
However, despite the various issues, it's believed some of the more reticent countries are being swayed by the financial package on offer from World Rugby.
The Nations Championship is being backed by a £5bn investment from sports marketing giants Infront.
For example the Rugby Football Union are thought to be open-minded, especially in light of the worrying financial picture at Twickenham.
The World Rugby council consists of 51 members across various rugby territories.