Access to the line would get activated by the IMF Board in a situation of generalized liquidity shortage (as, for example, when policy tightening in source countries after an extended period of low rates causes investment managers to become risk averse). In turn, the Fund could finance this liquidity by intermediating swaps with central banks (and thus guaranteeing central banks against default).
Such proposals allow countries access to liquidity without the stigma of approaching the Fund, and without the conditionality that accompanies most Fund arrangements, and thus are more likely to be acceptable as precautionary measures.