They will not be able to get around know your customer laws. I don't know why people insist on thinking that they can get away with money laundering if they rub a little crypto on their financial transactions.
How is this different from the "digital coins" e.g. gems in pay to win games then? They don't give me a bank account, but it's still digital money, but not a cryptocurrency.
Many businesses exclusively accept WeChat and Alipay. So there is a mechanism for paying rent, utilities and tax. Otherwise they would run out of cash.
To replicate that level of success, Facebook must create a mechanism to convert tokens back to cash.
So the tokens are basically just used to get past regulations. Facebook will then gather some hard numbers to show that crime is negligible. Sensible governments will tolerate the tokens because it's replacing physical cash where crimes like tax evasion are rampant.
A block chain will make it easier to build trust because (some) third parties can audit it.