Technically the only way Bitcoin can threaten the
very rich is if it directly undermines the value of their assets. How exactly will it do that if, right now, any one of them can sink a huge amount of USD into amassing a Bitcoin stockpile (either by buying lots of ASICs or buying them directly)? There are literal examples of this already - the Winklevoss twins have claimed to own over 1% of all Bitcoins, effectively converting some of their massive USD wealth into BTC. Even if you were to undermine the existing monetary systems, any rich person that saw it coming would easily be able to amass a giant BTC stockpile and ride it out. In that scenario, they would not stand to lose very much in a BTC transition, as long as they saw it coming before USD's value was completely destroyed.
The 'very rich' can afford to spend extravagantly to acquire bitcoins, and can afford to do so at 'a loss' if they actually have some good reason to convert money from other currencies to BTC. The average poor or middle-class person who has bitcoins to sell will be unlikely to turn down an offer to buy BTC at above market prices or similar other arrangements.
You can argue that Bitcoin is a threat to the revenue streams that the 'very rich' rely on to become wealthy and stay wealthy; however, it is mostly a threat in that it displaces those revenue streams. Speculators that currently work in things tied to USD can just as easily do their speculation against BTC; you do nothing to put those people out of work. Investors, likewise, are not somehow directly threatened by a Bitcoin-based economy. It's just currency to them.