When it was first drawn up nearly a decade ago, the plan to build out the heart of the Seaport District included a school, art gallery, branch library, several parks, and one very large performing arts center.

But over time, as the rest of the waterfront neighborhood has filled in and new economic realities set in, the Seaport Square project has trimmed the size of its parks and dropped plans for the school, library, and gallery. Now it appears the performing arts center could vanish, too.

The new owner of 13 acres of Seaport Square, Chestnut Hill-based WS Development, filed a revised building plan in February for nine blocks of housing, office space, and a tree-lined promenade from Summer Street to the waterfront.

But in one key departure from the original project approved by City Hall seven years ago, WS Development dropped a 200,000-square-foot theater from its building plan, saying it is instead considering a “cultural corridor” of likely-smaller venues.

WS said the switch was driven by changes in Boston’s cultural scene, where smaller spaces are more in demand than another giant theater.

But for some activists, the loss of the proposed theater is another sign of how the original ambitions for civic facilities and open space in the Seaport District have been reduced.

“We’ve seen it over and over,” said Hana Pegrimkova, a Fort Point resident who works with a small theater group in the neighborhood. “Promises get made, and then they change.”

Members of the city’s arts community said there is a much greater need for small- to medium-sized performing arts space than for the original proposal, which at 200,000 square feet would be a third larger than the Wang Theatre.

“What we’re seeing in Boston is that there’s insufficient space of that size — flexible space from 99, 250, 500, 750 seats,” said E. San San Wong, senior program officer for arts and creativity at the Barr Foundation, one of largest funders of cultural programs in Boston. “There are many organizations and individual artists who are at that smaller scale who could use that type of space.”

The theater was included in the master plan for Seaport Square that was approved in 2010, possibly as a new home for the Boston Ballet, which was considering a move at the time. The Ballet ended up keeping its South End headquarters and moving performances to the Boston Opera House.

In 2015 WS Development bought the remaining portions of the project, 13 undeveloped acres, for $359 million. The approved master plan, however, included an out for the large theater. It says the developer “could” build a performing arts center, and that it is “dependent on local demand and funding.”

“It wasn’t a requirement,” said Yanni Tsipis, the WS project manager for Seaport Square. “This was essentially a placeholder for this notional 200,000-square-foot performing arts center with a whole list of caveats and subject-to’s.”

With large performance spaces in Boston already underutilized, WS is instead surveying local arts leaders on their space needs. For now, the company’s proposal is vague. It has requested permission from the city to change the cultural-civic component of the project to a minimum 16,200 square feet, down from the 243,000 square feet approved in 2010.

WS Development partner Dick Marks said the company doesn’t want to commit to any particular amount, or type, of cultural space until it gets feedback from the arts community — which could take a year or more.

“We’re very open to meeting our cultural obligations, in a smart way,” Marks said. “What’s most important to us is building something that’s successful.”

The Walsh administration released a cultural plan in 2016 that identified a clear need for performance and rehearsal spaces, as well as affordable housing and studios for artists. The city is now wrapping up a more detailed analysis of Boston’s performance-venue needs.

The Celebrity Series of Boston, which uses various venues around Boston, from the 3,500-seat Wang to the 280-seat Pickman Hall at the Longy School of Music, could use something in between.

“There’s no middle ground,” said executive director Gary Dunning. “We’d look at something that size with interest.”

Another arts group in need of performance space is the Boston Lyric Opera, which is homeless this season after an 18-year run at the Shubert Theatre. The ideal size, according to Michael Puzo, chairman of its board of directors, is a theater of about 85,000 square feet.

“Boston has a need for a facility that is right-sized for a number of different users,” said Puzo, who recently met with WS Development officials over the arts space. “We’d be happy to be a part of a team of users that added some real vitality and creativity to” the Seaport.

The final say belongs to the Boston Planning and Development Agency, which held its first public meeting on the revised plan for Seaport Square Thursday night. Jonathan Greeley, director of development review for the agency, said the city wants “a significant cultural component,” but was wary of laying down specific requirements at this stage of the process.

“It’s not just purely about square footage,” Greeley said. “There are lots of ways for this project to leverage its momentum for the benefits of arts and cultural communities in Boston.

Corey Dinopoulos, a South Boston resident and activist, would like to see a “cultural corridor” throughout the Seaport District. Now a candidate for City Council, Dinopoulos said he wants whatever space is ultimately set aside in Seaport Square for arts to be written in stone — and the developer held to it.

“It’s going to fall by the wayside unless the city really holds them to some sort of specific proposal,” he said. “It needs to be more concrete.”