Excellent idea!
I'd suggest though to only really use the Steem Dollar balance for the credit card. Due to (Liquid) Steem being a deflating asset, people shouldn't really be holding Steem for any longer than strictly necessary, they should convert it to Steem Dollars (or Steem Power).
In the powering down scenario, the best would then be to convert powered down Steem to Steem Dollars, which you don't have to spend in hurry.