This one government agency would need to know the superset of everything about you that could possibly be reported on any tax form. The simple case breaks down quickly. If taxes were redesigned to become overall much simpler, then sure, the reporting could be much simpler and more passive for the filer.
Nobody is suggesting they create a government super computer that does every single person's taxes perfectly.
They're suggesting letting the irs actually use the resources they already have to automate the vast majority of the people's taxes to save everyone time and money.
It doesn't have to be perfect to be a huge improvement.
