HB's are pricing in a high chance of Bankruptcy. A big rate cut will not make HB's profitable over the next 18 months, but may be enough to stabilize the situation and make people think real estate is not going to fall 30% and that HB's are not going to go bankrupt.
With bankruptcy risk removed, many HB's could rally 30%+ as some are already trading at 1/3 or 2/5ths of book value.