Given how huge this hack is, and how little the BTC reward is going to be, I'm tempting to think this is either: - a test of a new hacking system - a demonstration to a big client - a first shot to threat some entity - a diversion while they get the real loot And that the BTC messages are just a way to justify it so it looks like a simple scam. Such a hack is worth way, WAY more than the few BTC it could bring.
Quite possibly this isn't a hack and someone got a Twitter admin's account, then got access to the admin panel and "all" accounts without having to hack much of anything.
If there is such a level of privilege in Twitter's stack, that says a great deal about their technology. Insiders must not be able to act as users except in prescribed ways requiring two-person control, logged and 100% audited. Glass-breaking privilege escalation should set off every pager in the company.