Agreed they don't have a solution in place that can do the calculations by mid-April. They do have a solution in place that could do it by late summer, so if people just opted-in (even online), the IRS could take it from there, and send a refund or a bill by Labor Day. For people with simple tax situations (not me, alas), that would be a boon to people.

I worry more about the tax law changes that might come if people started paying EVEN LESS attention than today about how their taxes are calculated than I do about the IRS ability to execute this.

Clicking a webform and getting a bill or direct deposit divorces people from the fact that this is real money in play.