Auckland Mayor Phil Goff wants to build a $1 billion stadium on the Auckland waterfront, calling Eden Park a "white elephant" that should perhaps be sold.
The idea for a waterfront stadium was brought up a decade ago ahead of the 2011 Rugby World Cup, but ditched in favour of upgrading Eden Park.
But Mr Goff says if Aucklanders want a bigger, better stadium, the planning has to start now - the railway land next to Vector Arena is the only suitable spot left.
"What a great place for a stadium," Mr Goff told Newstalk ZB. "When I look around the city, that looks to me to be the best option."
Mr Goff says Eden Park will need $250 million spent on it over the next 15 years, and its location - right in the middle of suburban Kingsland - means it can't host the number of events a city of Auckland's size demands.
"Putting that money into Eden Park would be a poor investment because of limits on time we can use that stadium," he told Newshub.
Mr Goff thinks it could fetch $300 million on the market, but that would only be a fraction of the price of a state-of-the-art new stadium.
"The private sector, I think, will come to the party to some degree, but also there is the opportunity again where we are going to have a national event where the Government is prepared to stump up and provide money like they did with the last Rugby World Cup," he told Newtalk ZB.
"Nobody believes that is the last Rugby World Cup we will have in New Zealand."
He's reportedly spoken to Warriors owner Eric Watson, who's expressed interest in the venture - as have Ngati Whatua and Vodafone boss Russell Stanners.
But former Rugby World Cup Minister Trevor Mallard, who offered Auckland $500 million to build a waterfront stadium in 2006, told the Herald on Sunday the Government probably wouldn't be so generous nowadays.
Mr Goff says it won't be "predominantly" ratepayer-funded.
Speaking to Paul Henry in March, Mr Key said the Government wouldn't pay for it.
"At a time when Auckland needs other infrastructure, turning around and saying the waterfront stadium's a priority would look a bit weird to Aucklanders - and the rest of the country."
Mr Watson said, also in March, the size of any new stadium would depend on what happened to Eden Park.
"If you're not keeping Eden Park, you probably need a Suncorp Stadium size, which is about 50,000 capacity. And you could do a lot better Suncorp -- you could have an amazing 50,000-person stadium," he said.
"If Eden Park's going to be around to cater for those very large, once- or twice-a-year opportunities, you probably have to go smaller."
Mr Goff says he hopes to have a firmer view on what could be possible by the end of the year.