Wouldn't self employed people and other legal citizens with odd jobs be able to use bank statements and tax returns and be fine?
Ever met anyone self-employed who wrote off everything from dog food to toilet paper? They may have a realistic cash flow of $5000 a month, but their AGI is $19400 a year. An underwriter uses the $19400 (plus some depreciation) as their income.
Now, there are loan programs allowing for using the average amount of deposits into a bank account for 12 months (called "bank statements" programs) but generally only subprime lenders allow this.