Assume some or all of the individuals in this list are saboteurs instead of defectors.
What types of attacks can they carry out?
What countermeasures are available to defend against those attacks?
They are not defecting. They are saboteurs (or allies depending on your goals) subsuming Bitcoin into the mainstream financial system and the plan for the NWO.
Very simple. They have monopolized the mining (ASICs concentrated into farms, 21 Inc, pools hidden behind Sybil attack) and the userbase (Coinbase, Paypal, Circle, Bitpay, etc). Checkmate.
Do you eat delusion for breakfast every morning?
P.S. Bitcoin will succeed in being widely adoped, because the elite want it to succeed. But they will be in control of Bitcoin. The decentralized, permission-less quality of Bitcoin will be a propaganda lie only, not reality.