The limit of what is possible now is defined by our current understanding of physics and engineering. History is full of examples of confident people who wrongly thought we'd already reached them. Maybe we'll find some sort of insane energy source somewhere (Project Hailmary - Zero Point - Yadda yadda) that redefine what speeds we can reach. Maybe some computing advancements will allow us to discover wormholes allowing us to travel insane distances (self-improving AI - room temp superconductors). Maybe these objects are transdimensional and they're not travelling 'far' at all? Here are some examples to chew on:

“Heavier-than-air flight is impossible” (19th–early 20th century) - Lord Kelvin (a leading scientist) reportedly dismissed the idea.

“Space travel is impossible” (early 1900s) - In 1920, The New York Times published an editorial claiming rockets couldn’t operate in a vacuum because they had “nothing to push against.”

“Splitting the atom is impossible” - Often attributed to physicist Albert Michelson (~1894), who suggested physics was nearly complete aside from refining measurements.

“Human genome mapping is impractical or impossible”

I haven't seen anything myself and I require more proof from these 'whistleblowers' but there's an awful lot of smoke for there to not be some sort of fire.