The basic issue is the current US property market is estimated at $33.6 trillion. If you assume 80% of that is land value you end up needing to compensate 26.88 trillion. On the other side of the market you have mortgages you put under water that people will walk away from. The mortgage market in the US is $17.6 trillion. If you assume 80% of mortgages are walked away from and the mortgages end up 70% underwater you end up having to compensate $9.856 trillion dollars. So solving the residential portion of compensation potentially costs $36.736 trillion dollars. If you have compensation in the commercial and industrial land markets as well that makes things even more expensive.
A tax credit that gets subtracted when the homeowner defaults equal to the value of the default would resolve the walk-away problem.
I agree you can modify how the tax credits work to potentially transfer the mortgage loss credits from the homeowner to the mortgage holder when the homeowner walks away. If you do this effectively you can reduce the cost by nearly $10 trillion but still have around $25 trillion in residential costs.
If we were to do an instant change, the best way to do that is to give everyone a tax credit equal to the value of their existing land, with retirees and others who need public support having a few more options to convert those tax credits to cash.