The prospect of transforming the matronly Hotel Pennsylvania — into an innovative office building with greenery draped over its numerous outdoor areas — just got rosier.

A new rendering of a future, 2.8-million-square-foot 15 Penn Plaza was quietly slipped into the tail end of an investor presentation by Vornado Realty Trust, the hotel’s owner.

Such a technologically advanced office tower could be developed on the east side of Seventh Avenue across from Madison Square Garden on the site of the current hotel that sits between West 32nd and 33rd streets.

If you follow real estate as a sport, you may recall that Vornado Chairman Steve Roth has been courting office anchor tenants to lease a replacement structure for almost a decade.

The original design for 15 Penn Plaza by Pelli Clarke Pelli was of a plump matron — showing deep cleavage but with no waistline to break up its 68 stories.

In 2010, the real estate giant persuaded the city that this proposed 1,216-foot-tall structure wasn’t going to interfere with the Empire State Building’s majestic singularity on the immediate skyline — just 900 feet away.

By 2013, Roth was days away from an inked agreement with Merrill Lynch when its chief resigned and took the deal with him.

Last year, we told you Vornado was presenting other design options to companies that included Morgan Stanley.

Now, what looks like a somewhat taller replacement seems to alternate sky parks overflowing with trees and plantings with blocks of office floors hoisted above them on giant pillars.

The fact that no leaves would survive the city’s legendary high-floor winds is immaterial — perhaps glass windbreaker partitions will aid in their growth.

Yet, both Silverstein Properties’ new version of Two World Trade Center, and Tishman Speyer’s Spiral in Hudson Yards, are also flush with outdoor spaces and greenery.

While both were designed by Bjarke Ingels Group, that architecture firm did not design this for Vornado.

Proposed replacement images for the Hotel Pennsylvania redevelopment

A similar design was created for L&L Holding’s upcoming 425 Park Ave. by Simon Davis of Rogers Stirk Harbour + Partners, although it’s just one-fifth the size of the proposed 15 Penn.

The Rogers firm did not respond to questions about the newest 15 Penn design, while the Pelli firm declined to comment and Roth simply ignored my requests.

One naysayer doubted this new design with expansive — and thus expensive — gardens would be built in the “inland” area.

“Experiments such as these are more commonly seen at the edges of the island, and even in the Hudson Yards district, most of the original architectural experiments with new forms got market-tested and value-engineered into pretty conventional buildings,” said one architecture guru who asked not to be identified.

Yet this is clearly a fresh, airy and Instagram-worthy design targeted to pique a millennial CEO’s imagination and kick off future-world New York.

The only question left is which tenant will pay sky-high rents to make it economically viable to tear down the 1.2-million-square-foot hotel and rebuild an engineering marvel that could cost $4 billion or more — similar to what other large towers now require — and be ready in four or five years.

“Two Penn and 260 Eleventh are certainly [Vornado] projects that people have confidence in them completing and are realistic,” said REIT analyst Alexander Goldfarb of Sandler O’Neill + Partners of smaller Vornado redevelopments in the pipeline. “[15 Penn] is one of those that could happen at some point in the future, but no one is betting their year-end on Hotel Pennsylvania.”

Nevertheless, when the time comes, any visionaries that decide to inhabit this next-gen Penn Plaza fairy tale will float skyward and likely tower over the new neighboring forests of Manhattan West and Hudson Yards.

Stay tuned.