Have you ever thought about building tax software for the other side of the fence i.e preparers? I'd love a chat about why the existing competition sucks and what's truly missing from the software market for tax professionals.
I heard from my CPA that Intuit provides very poor support for their ProSeries / Lacerte software, because they are trying to get everyone to use Turbotax instead. So even CPAs have a pain point that you could solve.
It seems like a domain a developer typically wouldn't have much insight into without a tax professional talking about it openly, or having worked on a product previously.
I find it odd that there are no free online tax filers in the US? TurboTax has a free version in Canada, and some competitors do as well. I like the idea though. Tax filing can always be made easier.(nevermind, a quick search shows that both TT and H&R have free filers.)