The numbers I came up with were based on a spreadsheet calculation that actually computing each year's income (based on 3.5% annual growth) and each year's deduction (based on 2% per year). I think it works out the way I said. However, if I'm missing something, the numbers could be tweaked (in terms of how many dollars of forgiveness you get per 0.1-point tax increase) to fine-tune it to the intended level (which, for me, is the level where it's clearly a good deal for most poor people, possibly a worthwhile deal for some in the middle class, and definitely not a good deal for the rich). If you think that wouldn't do it at a level of $1,000 of forgiveness for 0.1-point of tax increase, how about $2,000, or $5,000? At some point, you'd get a situation like I'm talking about.
You are asking people to give up a lifetime worth of income. As a financial advisor, I would never advise to take such a deal, though honestly, I was not much of a financial advisor.
It becomes an open ended debt, which would always worry me.