Two Questions for SAM

Andrew Caplin et al. propose a way to stop home foreclosures:

The way to do so is through the shared appreciation mortgage, or SAM. The concept is simple: Homeowners are offered the chance to write down a portion of their mortgage debt, but at the same time, they are required to share future appreciation gains with those who helped them out....

For example, a homeowner unable to support payments on a house purchased for $200,000 that today is worth only $150,000 might be offered a write-down of up to $50,000. But this would not be a free lunch.

With the SAM, once the value began appreciating above $150,000, the mortgage holders would be due their share. The details of the write down and the appreciation sharing could be tailored to different circumstances. But one way to give lenders a share of the upside would be to pay back some of the write down if the house is later sold.

This is like Zingales's Plan B.

I can see the attraction of these ideas, but I have two questions:

1. Would a law giving homeowners the right to write down their mortgages in exchange for equity attract so many homeowners that financial institutions would suffer even bigger hits than they already have? As these authors note, foreclosure is unpleasant for everyone. But because it is so unpleasant, some homeowners who are underwater on their mortgages keep paying them anyway. If we give them a better alternative, why would they?
2. If Congress were to pass a law allowing homeowners to rewrite their mortgage contracts, and lenders suffered losses as a result, what would the constitutional implications be? The fifth amendment says "nor shall private property be taken for public use, without just compensation." Could lenders get "just compensation" for losses that resulted because Congress crammed down an equity-for-debt swap? If so, would this be the best use of taxpayer funds?

Update: Andrew brings to my attention his longer, earlier treatment of the issue. He also responds to my questions. In response to the first question, he writes:

The offer would come from the lender (not borrower) in cases in which there is a stop in payment on the mortgage. Offering this on top of a standard write-down is an option that is currently not in their arsenal, a fact that many of them are not aware of (essentially ruled out by the tax code). One offers incentives for the writedown e.g. by exempting the shared appreciation strip from capital gains taxes. This is then part of the workout routine that would be far more attractive than a pure write-down, and often superior to enforcing default.

Suppose someone stops payment on their mortgage without needing to just because this offer is potentially open. They can be offered some powerful discouragement: (a) Increasing share of appreciation with increasing write down; (b) Give lenders ability to check income. There would then be a high % dedicated to the loan (you won't want this if you are doing fine or expect to recover income); potentially, have payments on the mortgage rise with income if one needs to work this angle harder.

The complete incentive system could be designed in a dynamic manner, adjusting as evidence of excessive use came to light.

In response to the second question:

This would be voluntary negotiation. The idea would be to set up the incentives for it in the tax code. It simply dominates current options in most circumstances.

Thanks, Andrew.