Exclude a mortgage for your primary residence, capped at the median house price or something… And only exclude it IF it is paid back in full over a max period.

This is the case in the Netherlands… paid back in full after max 30 years… No cap in how much. This was because the interest on the mortgage are tax deductible. So some bankers figured… we keep the loan maxed, and put your paybacks in a special fund… and at the end of the 30 years the fund pays back the mortgage. That way we get max interests and you get max tax break. In the end the banks made a lot of public funds private this way.