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.
In either case the tax prep industry is a pox on our society. But of course this is America, and replacing a perfectly functioning publicly accessible service with a nightmare of private sector bullshit is the most violently American shit ever.
Anyway, my point is that for 95% of people they have all the information already and you shouldn’t have to file.