The IRS switched to an xml file format a couple of years ago for e-filing, which broke the first week of the tax season. They were unable to accept any returns for around a week, IIRC. This article is a little overly optimistic about their chances of fully replacing tax prep, in my opinion.
The belgian government is so ineffective we didn't have one for two years because they failed to organize a ruling cabinet after elections. And still we have prefilled returns that work well. It's not that difficult.
