Why do you believe that TurboTax is horribly coded? I can't say whether or not their code is good or bad, but the US tax the fact that TurboTax is so popular and successful is only because the paper + accountant alternative was so terrible. I was describing an business app I've been working on to a non-technical friend, and she commented, "whatever you do, please make it as easy to use as TurboTax."
There was an interesting article posted on HN on how Intuit manages its 10 million lines of code for QuickBooks. I wouldn't be surprised if TurboTax is built in a similar fashion.
https://news.ycombinator.com/item?id=4315578
I'm not sure how terrible paper+accountant is/was, but TurboTax is just so damn convenient. I can do file my taxes on my lunch hour, at 3:00am, or while I'm on a webex at work.
They're instantly submitted (or at least they appear to be) and combined with direct deposit I get my refund within days. In the old days I had to either drop my paperwork off at an accountant and wait, do them myself and mail them in, or make an appointment with a preparer.
There was an interesting article posted on HN on how Intuit manages its 10 million lines of code for QuickBooks. I wouldn't be surprised if TurboTax is built in a similar fashion. https://news.ycombinator.com/item?id=4315578