I don't see a material difference or impact there. It was always assumed that they'd go to zero MBS.
In my view, the issue is whether they go back to printing or not. A flat balance sheet would still be a grinding disaster considering the onslaught of average $100 billion per month in new Treasury supply.
Here we have a rally based on hopium and driven by a massive increase in leverage, not permanent (or semi-permanent) central bank money.