It would be impossible for one person to accumulate all bitcoins unless they had dropped to essentially zero due to a devastating flaw/security issue.
Why impossible? Because every marginal bitcoin which is purchased from some other owner will increase in value up to infinity. Imagine if one man started buying all the bitcoins now... the price would rise and rise and rise. Perhaps he could get half the bitcoins. Maybe 80% of them. But as he approached 100% ownership, those with the remaining coins would only sell at higher prices. A bitcoin would become so expensive that not even Warren Buffet could purchase the last few.
Note: this same economic concept is why the world will never "run out" of oil, or trees, or any resource. If the last barrel of oil were found... at what price would it sell? Infinity. And long before that last barrel, alternatives would be used.
So cheer up all, we'll never run out of oil, and Bitcoins will never all be owned by one person
"A bitcoin would become so expensive that not even
Exxon could purchase the last few."