We've had something like this *online* in the UK for years, a dead-tree "self assessment" form for decades and even before the modern "self assessment" anybody could still file their own tax return for free as long as they were capable of presenting it clearly. Plus, if you're a simple wage slave with savings interest and other income below the threshold, everything is taxed at source and you don't need to fill in a return at all.
Here's the thing, though: we are still all perfectly at liberty to pay an accountant to do our taxes if we think they'll do a better job - and, of course, if you have complex tax affairs that is probably the case.
From what I've heard, though, the US IRS makes the UK HMRC look like a cute fluffy kitten who just wants to be your friend... which is quite an achievement since the HMRC can be pretty awful (e.g. go google IR35).