The Treasury's borrowing costs have been coming down lately, as investors all over the world dump risky assets and pour money into Treasury bonds. Since December of last year, the yield on 10-year Treasury bonds has fallen from 4.1% to 2.7% (as of December 5th). That's the lowest rate in the last 50 years, by a good margin.
Meanwhile, 30-year mortgage rates have remained stable. When the subprime loan crisis started making headlines in 2007, mortgage rates were in the low 6%-range. They've fallen since then, but are still within 0.75 percentage point of their pre-crisis levels. In contrast, 10-year Treasury yields have fallen by almost three times that amount.
With Treasury yields falling and mortgage rates remaining stable, the interest rate spread between the two classes of securities has increased to levels that haven't been seen in the last twenty years. (This is one of the primary indicators of distress in the credit markets.) From 1987 to 2006, the average spread between 30-year mortgages and 10-year Treasurys was 1.6 percentage points. Today, the spread is 2.8 percentage points. It hasn't been that high since the early 1980's, when inflation was running rampant.

Banks will have to be recapitalized in order for that to happen, but I don't think we'll have to wait for home prices to stabilize. (During the housing market downturn of the early 1990's, the mortgage spread actually fell below 1.5 percentage points.) Even if the Treasury plan is abandoned, there's a good chance that we'll see 30-year mortgage rates below 5% within the next year.