The vision imagines connecting the forthcoming western metro line – which terminates at Hunter Street – with a future south-east metro line,and a new station near Riley and Stanley streets below a 24/7 entertainment and hospitality precinct.

A revamped William Street,with high-rise offices and shops loosely modelled on Singapore’s Orchard Road,would turn it into “a remarkable boulevard,rather than the trashy artery it is now”,Cortese said. Rezoning the surrounding area for a significant uplift in development would also help pay for the project,which he estimated to cost $2 billion.

Grimshaw has quietly circulated the proposal among developers and the city’s leading cultural institutions for years. Sydney Opera House chief executive Louise Herron told theHerald it was a “beautiful idea” and “fabulous concept”,although she said the design of the performance halls should be put out to a public design competition.

“It’s a really good use of the space,and when you look at really great cities,they manage to have joined enlivened spaces. We still have quite a few dead patches,” she said. Herron was sceptical of whether Sydney needed another concert hall,saying flexibility was key.

“There’s no doubt the current demand is for excellent,unmissable work. That’s what people are coming to,” she said. “You can’t pick the genre,but you can pick excellence. We need spaces where people can gather,and spaces with appropriate equipment.”

Committee for Sydney chief executive Gabriel Metcalf – also briefed on the proposal – said it was an exciting vision for east Sydney,although it would be vital to work through the details with the city’s existing cultural institutions.

“The Domain is part of the spiritual core of Sydney,so you have to always be really careful when you’re working in and around the Domain,” he said. “But previous generations of Sydneysiders already made the grave error of putting the motorway right through the middle of it ... there are some mistakes from the past that need healing.”

Sydney has long grappled with its need for a new theatre and absence of a theatre district,and last yeartheHerald revealed the state government was scouting old picture palaces for potential sites.

Grimshaw is portraying its concept as the better option because it would centralise the venues and start much-needed renewal of east Sydney and Woolloomooloo. “We can’t have an under-utilised part of our city within a 500-metre distance of the centre for the CBD,” Cortese said.

The architect’s briefing paper says Woolloomooloo is experiencing the “early stages of incoherent gentrification”. Under the proposed vision,old public housing would be upgraded and new stock added,while new open public spaces would include a raised walkway and cycleway above the existing heavy rail line that slices through the precinct.

Cortese said William Street was ideally positioned to serve as the epicentre of a renewed 24-hour district,which would never return to Kings Cross. “It’s a fundamental transformation of how the city works.”

The proposal has no government endorsement at this stage. “It is just us advocating for an idea ... but the debate about it must begin now,” Cortese said.

Grimshaw,a London-based architectural studio with a Sydney office that opened in 2015,has designed projects such as Melbourne’s Southern Cross Station,Sydney’s light rail stops and the forthcoming Martin Place metro station.

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