Don't think it would sit so well in Sydney and Qld though. Too incompatible with the established comps and traditional set-up.
In terms of Sydney: there are a few clubs who would gladly knife the rest if they could make a quick buck from a national comp.
The Premier Rugby competition (sometimes referred to as Shute Shield but that is just First Grade) consists of (currently) 11 clubs with 4 Senior Grades and 3 Colts Grades each... well in theory.
Randwick, Eastwood, Sydney Uni, Gordon, and Eastern Suburbs have enough players for probably 5 Senior Grades and 4 Colts sides. Maybe more. They warehouse a lot of guys so they can take rego money off them every year. Easy money from idiots who are happy to get a pair of shorts and socks, and sit on the bench for 10 minutes every other week.
Northern Suburbs, Manly, and Warringah probably sit in the next tranche, with Norths in particular having issues fielding all 3 Colts sides this year. Warringah's Colts were good, but Grade were duds in 2023.
Hunter Wildfires (based in Newcastle) are only in the comp as a rescue mission* and only field 2 Grades + 1 Colts - they might not be there next year, because the Newcastle comp is also suffering and they can't get the numbers, and the travel is a bit of an issue.
*Penrith were slowly imploding but they wanted 12 clubs, so Hunter stepped in. Then Penrith left to go play in Canberra, where they also got smaaaaaaaaashed
West Harbour and Southern Districts fielded all their teams but mostly got whipped.
Two Blues could only field 3 Grades + 2 Colts (struggled to do that) and their results were ordinary. First Grade finished mid table (9W, 9L), Second Grade bottom 4 (7W, 11L), and Thirds stone cold last (1W from 17). Their Colts failed to win a single game between them. I'm shocked they haven't fallen over.
So, with the top 4-5 clubs in Sydney, and 3-4 from Brisbane, and one each from Canberra and Melbourne, you could create a decent competition BUT funding it is the issue.
Besides bus trips between Sydney and Canberra, everything else is a flight. If you want to include Perth, it is an expensive flight.
We don't exactly have billionaires lying around to fund this (besides Twiggy) so it'll need some creative thinking to work.