Why?
I mean, presenting a specious premise such as "the government sector is incompetent" ignores the fact that whatever private company which offers tax preparation must, by definition, interact with IRS systems.
Unless your premise is that one or more startups can replace federal tax collection.
> There are plenty of dev companies capable of doing this and doing it well.
The position argued by both @Obversity and @tlb is that somehow "private companies" can satisfy what the IRS is required, by statute and Congressional oversight, to provide. "Private companies" are not subject to such constraints.
Hence my reductio ad absurdum conclusion of:
> Unless your premise is that one or more startups can replace federal tax collection.
IMHO this implies they will also be unable to create a meaningful tender and evaluate the results.
The hardest part of writing this kind of software is not the coding, but getting all the details right.
There's no reason they couldn't contract a private company to build the system, perhaps with a hand-over plan at the end of it with advice on how to build and manage a development team to maintain it in-house.
There are plenty of dev companies capable of doing this and doing it well. Put it up for tender.