The old pier behind the Blue Hills Bank Pavilion looks much like it has for three decades: unused, dilapidated, forlorn. One of the last empty waterfront properties in Boston, with front-row views of the skyline and harbor, it remains fenced off from the public.

While the surrounding Seaport neighborhood boomed, the pier, known as Dry Dock #4, had few serious proposals over the years that capitalized on its location: The late mayor Thomas M. Menino once floated the idea of a new City Hall on it, while state and city officials later suggested installing a helipad in the area, partly for General Electric’s use.

But after a conservation group and a developer each proposed unusual plans for the 6-acre site, highlighting its potential, the Walsh administration took a second look at Dry Dock #4 as a place for the public.

As part of a review of properties in South Boston’s waterfront industrial park, the Boston Planning & Development Agency has proposed relaxing restrictions that limit Dry Dock #4 to commercial marine and port activities. With City Hall under fire from some quarters over the lack of parkland in the Seaport, the Walsh administration has said it will solicit proposals this spring for public use and open space on the dry dock.

“I would hope that those contemplating uses would certainly focus on parks and open space,’’ said Richard Taylor, director of Suffolk University’s Center for Real Estate. “This is a great opportunity to fill that gap, to fill that void. . . . For the Seaport to be regarded as a neighborhood, you need additional spaces like that.’’

Earlier in 2017, the Trustees of Reservations had considered building a park on the pier. But at the urging of the Walsh administration, the venerable conservation group is prioritizing plans for park space along Fort Point Channel.

And more recently, a group of entrepreneurs proposed expanding on the Trustees’ idea for Dry Dock #4 by using the main structure as a public open space, but docking a cruise ship next to it that would serve as a floating hotel with 300 to 500 rooms.

It’s possible both ideas could coexist. The hotel development group has been in communication with the Trustees about their respective plans. But for now, each is working separately. They both expect to submit proposals once the city’s solicitation is released in 2018. And other bidders could emerge.

The cruise-ship idea isn’t new. It surfaced even before Menino’s short-lived plan to move City Hall to the pier. Brent Johnstone said his partner in the venture, Tim Allcott, first approached the Menino administration with the idea about a decade ago.

Johnstone and his partners revived the idea after a helipad on the dry dock for GE and other corporate travelers was shelved because of neighborhood opposition earlier this year. They formed a business, Boston Dockside Group, and have sounded out investors and hospitality operators.

He envisions converting the pier into a marine terminal that could also serve water taxis and recreational boaters. There would also be an extension of the Harborwalk pedestrian path, but Johnstone’s idea for converting the remaining portion of the pier into open space is less developed.

“We’re going to try to get as creative as we can to make sure that we make it a fun place for people to go,’’ Johnstone said. “It will provide stunning views of the city.’’

He argued the ship could provide much-needed hotel rooms within walking distance of the Boston Convention & Exhibition Center. It could also liven up a rotting piece of infrastructure that until now has been a bit of a puzzle for city officials. They will probably need backing from South Boston’s elected officials. State Representative Nick Collins and City Councilor Michael Flaherty both said they see the “flotel’’ as a creative idea that deserves further discussion.

The Trustees also view the pier as a cornerstone in their efforts to develop signature public spaces along the waterfront. Any park project there would be likely to require millions of dollars in funding and, as Nick Black, managing director of the Boston Waterfront Initiative for the Trustees, puts it, a “coalition of partners’’ to make it happen.

“It’s really a great opportunity for us to bring about a really nice public amenity to a part of a city that is arguably in need of some,’’ Black said. “There really aren’t that many opportunities left in the city to create that kind of space, directly on the water.’’

Much of the larger, nearly 200-acre industrial park is restricted by the state to marine-related uses. A proposed new master plan from the Walsh administration would allow a greater proportion of other commercial activities, while still maintaining a strong core of marine businesses, such as seafood processing.

But with little prospect of the shipbuilding industry bringing major repair work back to the pier, city officials singled out Dry Dock #4 for open space and public facilities.

“What we’re realizing is we’ve got too much real estate for the port economy,’’ said Richard McGuinness, deputy director for climate change and environmental planning at the BPDA. “We don’t need another dry dock.’’

The Walsh administration is awaiting state approval of its proposed changes at the marine park.

Preparing the dry dock won’t come cheaply. One side, facing the outer harbor, is in good shape after undergoing $2 million-plus in repairs recently, but the western, or downtown, side could cost at least $6 million to fix.

Waterfront advocates said the park and floating hotel pitches for Dry Dock #4 underscore the need for the city to rethink the empty industrial properties along the East Boston and South Boston waterfronts.

“The broader question is, what is the highest and best use of the remaining parcels that are on Boston’s waterfront?’’ said Jim Canales, president of the Barr Foundation, which helps fund public use and waterfront projects. “What are the ways we’re ensuring we create a waterfront that is accessible and a waterfront that is resilient?’’

Yet others caution that the pendulum should not swing too far in the other direction, by neglecting the commercial marine uses that have defined the waterfront for centuries.

“Development pressures absolutely have a lot to do with this,’’ said Deanna Moran, director of environmental planning for the Conservation Law Foundation. “But there are uses that can . . . help service the public and also preserve the option where, if we needed, it could be converted back to maritime uses.’’

Jon Chesto can be reached at jon.chesto@globe.com. Follow him on Twitter @jonchesto.