we already see collusion from the biggest bitcoin businesses in the industry. I'd say we are already half way there. You don't have to own all the bitcoins to own the market, you just need to control the vast majority of the ins & outs of bitcoin in order to exert control over it. We've seen this with the mining industry, exchange industry, bitcoin news industry, moderator positions, etc.

It's in a business man's best interest to get as much of the market as possible under their wing, purely for profit reasons.

In example, they didn't have to buy up all the gold in order to control the market... we've seen collusion in the spot prices of gold for 50+ years now among international banks, it's called "the fix" and even though it is completely legal, it has been abused countless times. Some of the biggest names in the banking industry recently settled for millions of dollars over manipulation of gold prices...

http://heartlandpreciousmetals.com/deutsche-bank-admits-it-rigged-gold-prices-agrees-to-expose-other-manipulators/

banks = exchanges, exchanges = banks. It's just a new descriptive word for something we've had for 100s of years now. The one "shining" difference between bitcoin exchanges & banks is exchanges aren't mean to store your money on, just exchange, even though people still use them as storage (aka banks).