I have a probably stupid question: given that the IRS killed Direct File, even if your software can create ready-to-file (or even ones that need some work) tax returns, isn't that moot without a way to like... get the IRS to accept them?
Why wouldn't the IRS accept a tax return created by your own software? How would they even know it was custom software? Ultimately your tax return is just a stack of papers that gets sent to the IRS.
Software sending efiles to the IRS has to be tested with and approved by the IRS. The IRS is working toward eliminating paper filing as an option. At this point, paid preparers are legally required to efile all returns and if the return gets rejected and they must paper file, they have to include Form 8948, Explanation for Paper Filing. For the IRS to accept a tax return from software the software has to go through this process.
https://www.irs.gov/e-file-providers/how-tax-preparation-sof...
You can use free file fillable forms to submit online. It's a bit of work to transcribe from other software. It also requires a particular interpretation when filling forms (e.g. you need to round before summing your W-2s).