Maybe 2017 is a bad example, but say at the end of 2018 they have a net worth of $75B. They make a payment of $72B to treasury, retaining a $3B net worth.
Then in Q1 the following year they have to mark down mortgages due to market changes, and their net worth is negative $5B. There wouldn't be a payment due, but their net worth would still fall negative, meaning under current rules they would need a draw.
I guess the plan is to change the 60-day negative net worth rule to 1 year too? That seems risky.