A quieter street

In the Costa scenario, trading changes completely.

In a future world where cash becomes marginalized and digital "credits" take over as a system of payments, companies find old-fashioned stock issuance a trite method of raising funds. Stocks, meanwhile, start to more closely resemble mutual funds, with very little if any price movement during market hours and instead "a final pricing at the end of the day," Costa said.

"There will be more financial options for investors," said Todd Schoenberger, managing partner at LandColt Capital. "For example, we now have stocks, bonds, mutual funds, etc. Look for new products to enter the market, which will be a real hassle for regulators. But, expanded options is what you get when you have too many players transacting business."

Whatever form trading takes -- high speed, low speed or no speed -- what will matter most is fairness, and many Wall Street pros expect Washington regulators to continue their pursuit of an equitable environment.

"What they're realizing is money managers like myself don't care about getting a sell in half a second," said Michael Cohn, chief market strategist at Atlantis Asset Management. "I don't care about the pennies, I care about the perception and the fairness. It affects my business if people think the market is not fair."

If there is a common theme in terms of hopes for the future, it indeed would be some simple fairness.

"You can still have automation, but it would be nice to bring back some sort of ecosystem into it," said Joe Saluzzi, co-founder of Themis Trading and an ardent campaigner against the ills of high-frequency trading.

Saluzzi hopes the next 25 years hold a greater emphasis on human involvement, not less.

"You like to have someone involved. The investor relations officer, the chief financial officer, really has no idea what's going on in their stock," he said. "There are no specialists involved. They need more information as to what's going on. It's not there anymore."

While the amount of bodies on the exchange floor indeed has dimmed considerably over the years, the level of employment in financial services has remained fairly and surprisingly resilient.

Financial services jobs peaked out in late 2006 at about 8.4 million, according to the Bureau of Labor Statistics. While that level certainly has declined, the nearly 6 percent drop to 7.9 million as of March 2014 could have been much worse considering the way Wall Street banks cut jobs en masse during the crisis.

A shift to markets abroad

Expectations, though, are for even fewer footsteps on the Street.

"The amount of employees that will be working on Wall Street, if you want to call it that, is going to continue to go down year after year," said Marc Pfeffer, a former trader at Goldman Sachs (GS) and the defunct Bear Stearns who now works as a portfolio manager at CLS Investments. "I am perplexed til today to understand why there are that many people at these firms. I think they're going to be cut by a huge percentage, if they even exist at all."

So where does that leave the exchange as a physical property?

If you close your eyes tightly enough you can almost see the tumbleweeds rolling across the cobblestones past the Wall Street subway station, past the Deutsche Bank (DB) building and gliding on a path to nowhere. After all, what possible use could there be for such a structure in the next age of trading?

"I don't think the NYSE exists anymore period," said Dick Bove, the outspoken banking analyst and vice president of equity research at Rafferty Capital Markets. "I think it's a good television set for you guys."

Well, there's that. It's true that on some days the most excitement comes from the guests that CNBC and other media attract, whether that's market veterans like Kenny Polcari, CEOs such as AIG's (AIG) Robert Benmosche or professional celebrities like Kim Kardashian. But is it possible the building will serve no function?

Bove sees the global financial center shifting from New York only to various other places around the world -- Canada, China, wherever countries are committed to a thriving banking sector and not obsessed with handcuffing "too big to fail" institutions. He also points out that the exchange isn't even owned by a New York firm anymore, and that most of the trading happens at high-frequency nerve centers in New Jersey.

Other challenges New York faces include its inability to attract technology-focused industries, intensified regulation from city and state politicians, and the rise of financial centers around the world that will provide major competition.

All those factors, he said, will make the NYSE, if not obsolete, at least substantially declining in relevance.

"It's a historical oddity. It should be given to one of the historical preservation societies," Bove added. "It does not exist today. It will not exist in 25 years."

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