Commercial real estate analysts warn that the amount of sublease inventory in top US markets is at or now exceeding levels of the Dot Com bust and the Great Financial Crisis. 

Bank of America and SalesForce are the latest companies extending remote working options for employees. These analysts now believe the office space market may not recover even though the broader economy rebounds. 

Daniel Ismail, the office analyst at Green Street Advisors, a real estate research firm, said the country "just underwent what will end up being close to a year-long work-from-home experiment, and the results continue to show for themselves."

"You have a company every other week saying how successful work-from-home has been for them, and their plans to reduce or shrink their total office space needs," Ismail said. 

He believes that demand for office spaces could be down 10 to 15% even after the economy recovers, adding that rents in top markets such as New York and San Francisco will continue to experience declines in 2021. 

Ismail said work workplace changes (remote working), which were supposed to take 4 to 5 years to unfold, are happening in a matter of quarters. 

"We're turning on a dime," he said.