Ready to dream?

And we mean really dream?

Then start by imagining a north-south light-rail line from Oyster Bay to Valley Stream, with an extension directly to the Nassau Hub. Picture mixed-use transit-oriented developments across Long Island, with multifamily housing replacing train-station parking lots.

Think of taking the train — one train — from Long Island to New Jersey and back. You’d pass through Jamaica and Sunnyside Yards, stop at a new station at Third Avenue and 31st Street in Manhattan, then at a redeveloped Penn Station, and finally head through new tunnels under the Hudson River, stopping at existing stations in New Jersey.

Once in New Jersey, in this picturesque world, you might head over to the newly created Meadowlands National Park, saved from potential flooding and the impact of climate change with federal dollars and protection.

In this dream, there’s plenty of affordable housing. The subways are modern and wheelchair-accessible, though the system would be closed overnight. The shorelines are protected from rising sea levels, the power grid is new. The Metropolitan Transportation Authority and Port Authority of New York and New Jersey are bureaucracies that efficiently do what they’re supposed to do.

And how would you like a pony under your Christmas tree?

The Regional Plan Association, a well-respected research and advocacy group, emerged Thursday with its fourth regional plan in a century, a 300-plus page document that could serve as the ultimate utopian wish list. The plan does a masterful job of outlining the region’s shortcomings — focusing primarily on transportation, the environment and affordability — and arriving at dozens of extensive prescriptions to solve them. The report embraces development, growth, density, public transit and shoreline protection — all key concepts for a region that too often fights its own best interests. And with a 25-year timeline, the RPA is relying on a long-term strategy.

The big thinking, with a wide, regional lens, certainly is welcome — and rare. But its hodgepodge of more than 60 proposals lacks the innovative, specific big idea or two that everyone can rally behind. It’s as if the RPA threw every dart at every spot on a regional dartboard, rather than strategically aiming one or two at the bull’s-eye.

And it failed to provide pinpointed focus on Long Island. Other than the north-south transit line in Nassau, and continued attention to downtown redevelopment, there’s little new or revolutionary for Nassau and Suffolk counties. It’s disappointing that the RPA didn’t include a deepwater port in Shoreham, a tunnel or bridge from Long Island to Westchester or Connecticut, or additional north-south transit paths.

But it’s worth giving serious thought to some notions that seem more unlikely to happen — like the one-seat train ride from New Jersey to Long Island and a more integrated commuter rail system — concepts that could be difference-makers for the region.

Closing New York City’s subways every night is a nonstarter, but there are more realistic ideas in the report worth considering: Prioritizing the modernization of subway tracks, signals and stations, with a faster timeline and smaller budget, perhaps through a new public agency specifically tasked with responsiblity for city transit improvements. A regional coastal commission to deal with climate-change issues. More transit-oriented development, and housing in place of parking lots. And congestion pricing, with tolls on the East River bridges and entrances into midtown Manhattan, and perhaps some highways, to reduce traffic and provide funds for key projects.

But by going really broad, the RPA made it too easy for more practical, doable suggestions to get lost in splashy, easily dismissed proposals. Most of the RPA’s prescriptions would cost staggering sums of money — and plenty of political capital. The organization suggests funding mechanisms like congestion pricing, tolling highways, and adopting cap-and-trade policies similar to California’s.

RPA officials note that it’s important not to be fatalistic, not to assume that their ideas won’t ever happen. They’re right, but they go too far in discounting the region’s many political layers, the complicated bureaucracies that dominate our landscape, and the NIMBY attitude that too often blocks the political will to do anything big.

In the 1920s, the RPA proposed a bridge connecting Brooklyn and Staten Island, now the Verrazano-Narrows, and suggested that a crossing between Manhattan and New Jersey should be built farther north to connect a series of highways, now the George Washington. Since then, other plans planted seeds for the Long Island Rail Road’s East Side Access and Hudson Yards.

In a generation or two, how will others look back on the fourth regional plan? What will the success stories be?

Advocates and elected officials should spotlight what’s really possible. Get behind a few big ideas, and move them forward. The plan is a conversation-starter, not a final blueprint.

Just don’t count on the pony.