The quote came toward the beginning of Steve Kerr’s news conference at Warriors media day last month: “We’re well aware it’s not going to last forever.”

Within minutes, that nine-word sound bite rippled through the blogosphere, causing many to speculate about what exactly Kerr meant. Was the head coach suggesting that Golden State soon would make major roster moves? Was Kerr treating the coming season as if it could be the Warriors’ last as a championship favorite?

As is often the case with dynastic runs in sports, some NBA fans have become obsessed with forecasting Golden State’s demise. And the summer of 2019 is a good starting point. Of the 13 players currently on the Warriors’ roster, seven — Kevin Durant, Klay Thompson, DeMarcus Cousins, Jonas Jerebko, Kevon Looney, Quinn Cook and Jordan Bell — will hit unrestricted free agency in July.

Because of how their contracts are structured, Shaun Livingston and Damian Jones also would become free agents if Golden State decides those two aren’t worth keeping on the team’s massive luxury-tax bill. Andre Iguodala, who turns 35 in January and is guaranteed $17.1 million in 2019-20, might not be in the Warriors’ plans past this season.

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Golden State’s payroll could spike into the $300 million range before its first game at state-of-the-art Chase Center in San Francisco. Then comes the summer of 2020, when the Warriors will have to decide whether to bring back Draymond Green on an annual salary that could start as high as roughly $38 million.

Stephen Curry, who is only a season into his five-year, $201 million deal, is the lone player whose future with the Warriors is settled beyond 2019-20. Though it’s possible that Golden State will remain the class of the league for several more seasons, the financials alone make that tricky.

And that is before factoring in other important considerations.

With Durant, Curry, Thompson and Green each at or near age 30, the Warriors’ core soon will test the limits of its prime. Even if Golden State can keep those four together (Cousins is almost definitely a one-season rental because of salary-cap restrictions), the team has no guarantees that Durant, Curry, Thompson and Green can avoid the drop-off in production that hits many players in their early 30s.

There is also the matter of motivation. Last season, the Warriors wrestled with complacency before eventually living up to their potential in an NBA Finals sweep of Cleveland. Getting up emotionally will become only more of a grind the longer Golden State plays into June.

Then there is the fact that the talent divide separating the Warriors from the rest of the league has tightened. Though a recent NBA.com survey had 87 percent of general managers picking Golden State to win a third straight championship, it faces viable threats in the Rockets, 76ers, Raptors and Lakers.

However, no franchise is more capable of dethroning the Warriors than the Celtics.

Had it not shot 7-for-39 from three-point range in Game 7 of the 2018 Eastern Conference finals without Kyrie Irving and Gordon Hayward, Boston would have become the first team from the East in eight years to eliminate LeBron James from the postseason. Now, with Irving and Hayward back from injury, the Celtics are the clear favorites to make it out of the East.

It is not out of the question that Boston could eclipse Golden State as championship favorites within a year. In addition to having three All-Stars in Irving, Hayward and Al Horford, the Celtics boast two young phenoms in 20-year-old Jayson Tatum and 21-year-old Jaylen Brown and one of the league’s best head coaches in Brad Stevens.

Kerr is keenly aware of all of this, which is why he has made a point to encourage his players to enjoy the moment.

“I don’t think our guys should feel a ton of pressure,” Kerr said. “I think they should feel the importance of trying to do it again, because this may be the last time we have this current iteration of the Warriors.”

Added general manager Bob Myers: “I have to remind myself that this is such a rare time for our organization to have this kind of talent. ... To watch Kevin Durant and Steph Curry right here do a shooting drill, I don’t take any of that for granted.”

What the Warriors have built is historic. Regardless of whether it becomes the first franchise since Bill Russell’s Celtics in the 1960s to reach five NBA Finals in a row or win four championships in five years, Golden State will go down as one of the league’s greatest teams.

In late September, when Kerr said at media day that the Warriors’ reign atop the league wouldn’t last forever, he wasn’t being incendiary. He was stating the obvious. There is a reason why none of the NBA’s modern dynasties — not the 1990s Bulls, not the Lakers or Celtics of the 1980s, not the Tim Duncan-led Spurs or the Kobe Bryant-led Lakers — have even flirted with the Celtics’ 11 NBA titles in 13 years half a century ago.

Long gone are the days when it was commonplace for elite players to spend their entire careers with one franchise. Because of the NBA salary cap and many All-Stars’ desire to chase the next big opportunity, dynasties are increasingly rare. If Golden State hoists its third consecutive Larry O’Brien trophy in June, it will be the first team to do so since the 2000-02 Lakers.

“I think this year is going to be a fun, exciting season,” said Durant, who has already seen reports that he could sign with the Lakers or Knicks next summer. “We’ll see what happens after that.”

Connor Letourneau is a San Francisco Chronicle staff writer. Email: cletourneau@sfchronicle.com Twitter: @Con_Chron