Yorba, the IRS, and tax-exemption

You can challenge IRS interpretations quite easily. You have to go through the appeal process but you can still challenge them in court if the appeals don't go your way. The IRS has been trying to crack down on what they believe is abuse of the 501c category without special authority from congress to do so. Though the IRS has broad rule making authority such rules and interpretations are subject to review and rejection, it's just a harder and more involved process.

If this becomes more widespread as a broad rule from the IRS I would imagine at some point that someone it going to have to challenge this in court and force the IRS to recognize FOSS software as a public benefit. Hopefully the appropriate foundations can put the wheels in motion on this before it becomes a life or death situation for them.