David Henderson rounds up links to various economists and think tanks that have studied the Romney tax plan. They all agree that it's not impossible, that it could work, and that it is very similar to the Simpson-Bowles plan (which President Obama summarily ignored).
After laying out the details of the Romney plan, Reynolds does a comparison:
When it comes to tax policy, the main difference between Romney's and Obama's National Commission on Fiscal Responsibility and Reform and Bipartisan Policy Center's Debt Reduction Task Force advisers is that Romney proposes 1) a slightly lower corporate tax rate, and 2) a much lower bottom rate of 8 percent rather than 12 percent. (The fact that there would be six rates rather than three is insignificant.)