I know people in the government too. They're all passionate and loyal workers, often taking a job because they believe in the greater good as opposed to making money.
But 18f is a relatively small project (~100 employees), and overall USDS is relatively new. Veteran's Affairs for example STILL isn't digitized and is almost entirely a paper-run system. USDS is likely going to focus on that as opposed to building out a new website for the IRS.
Just realistically speaking, the kind of project you are proposing will take years to deliver version 1.0, and there's no guarantee that the USDS team will even handle it as there are definitely higher-priority tasks.
You are grossly overestimating the US Government's capabilities. I'm not lying when I say that the US Government needs to
1. Create a budget (we're still under continuing resolutions here. A budget hasn't been passed since like 2012)
2. Raise wages for once to attract talent (it has almost been a decade without wage growth, very bad for morale). FYI: the government shutdown threats (ie: federal employees / contractors don't get paid randomly) aren't helping.
3. Build up the IT teams, and I mean more than just a single 100-man team at 18F. The entirety of 18F, as good as they are, are way too small to handle a project on the scale of "Recreate Turbotax for All Americans... for free".
4. Build up project managers in the meantime who can handle contractors.
5. Hire competent contractors to build things out.
6. Execute all the above while Congress continues to refuse to pass a budget and the Republican half of America seems like they're going to lynch "greedy" Federal Workers who don't actually have great pension plans anymore (only the older Federal Workers have the crazy-good pension plan. Any millenial / college age kid who gets hired by the Feds don't really see as many benefits)
There are some fundamental problems here that need to be fixed before the US Government can tackle a project like you say successfully.
EDIT: one of the leading Presidential Candidates (Ted Cruz) is on the record for wanting to "Abolish" the IRS. People in general don't like Federal Workers, and that harms recruitment efforts. Which harms the kinds of project you want to start up. Its partially a self-fulfilling prophecy at this point.