Technically, the use of the software isn't compulsory. You can still fill out the physical tax forms and mail them in.
That said, I am solidly on board with the IRS just computing the taxes for taxpayers and sending them a bill. Taxpayers who dispute the bill can then just file their own taxes as normal.
All your financial transactions are already reported by the other parties (including most foreign ones: I have an offshore account that reports to FATCA).
Your personal data (age, dependents, marriage) is also in databases recording births and status changes.
That said, I am solidly on board with the IRS just computing the taxes for taxpayers and sending them a bill. Taxpayers who dispute the bill can then just file their own taxes as normal.