Southern hemisphere rugby bosses have cautiously endorsed the latest developments in the Nations Championship saga, with Rugby Australia boss Raelene Castle calling discussions "exciting but complex".

World Rugby and the SANZAAR nations had a major win overnight in Dublin with the top tier nations agreeing to further discussions over a $9.4 billion broadcast offer for the proposed 12-team competition.

The Nations Championship proposal has survived a crucial test at World Rugby meetings in Dublin this week. Credit:Hannah Peters

Fears the concept would be killed off by a $937 million private equity offer, from former Formula One owners CVC, for a stake in the Six Nations were not realised - not yet anyway.

London's Daily Mail reported that all unions faced a March 29 deadline to agree to the proposal, with third party negotiations - presumably including the CVC group - off limits after that.