Bitcoin is already not legal tender. Legal tender means you are _obligated_ to accept it as payment for a debt (eg, in the US, a lender cannot refuse a payment

Bitcoin is already not legal tender. Legal tender means you are _obligated_ to accept it as payment for a debt (eg, in the US, a lender cannot refuse a payment on a debt in dollar bills). It does not _necessarily_ mean that non-legal tenders _cannot_ be used for barter.