Mr. Zahid also manages another boutique, on Fordham Road in the Bronx, which is near a subway stop. “We have very good business there, why? Because you get off the subway, and you have the store,” he said, as he stood inside the store on East Tremont Avenue. “Here? Look, empty.”

Rectifying the disparity of access would take more than 60 miles of new subway track and over 40 new subway stations, according to the Regional Plan Association. The association did not estimate what such a proposal might cost, but as a measure the roughly one-and-a-half-mile stretch of the Second Avenue subway that opened this year on the Upper East Side of Manhattan cost $4.5 billion, or about $2.7 billion per mile.

The Regional Plan Association says that the added capacity for growth that new subway branches would bring could fund construction with new taxpayer revenues. Things like congestion pricing, charging drivers a fee for traversing parts of the city, or value capture, when real estate development enhanced by new access to transportation chips in could also be sources of funding, according to the association.

While the organization’s proposal may seem unrealistic, it was designed to spur discussion and to look far into the city’s future, said Dani Simons, a spokeswoman for the association. In producing the report, the group sought, she added, to “not be limited to thinking about what is achievable today, what is achievable in one year, but to think about what we really need in the bigger picture to move our city and our region forward.”

Officials with the M.T.A. declined to address the feasibility of the proposal. “We are restoring the subway system to a state of reliability and at the same time taking on vital long-term expansion projects,” Jon Weinstein, a spokesman for the agency, said in an email.

One major project involves extending the Second Avenue subway northward, which the Regional Plan Association says is vital to better serving neighborhoods in Manhattan. The transportation authority has set aside about $1.7 billion to pay for part of the cost of the next leg of the Second Avenue project, which will reach from 96th Street to 125th Street, though no timeline has been established, and the source of funding for the rest has not yet been identified.

Enrique Toledo scoffed at the idea that there would ever be any major subway expansion beyond what is already in the works, especially to serve the city’s poorest residents with the least political clout.