This reminds me of the challenges faced by (micro)computer user groups in the mid-to-late 1980s, as they grew to the point of seeking 501c3 tax status, under some of the same body of law.
Lawyers told us the authoritative precedent (PDF) at the time (remember, we couldn't Google it) was a 1974 vendor-specific minicomputer-platform user group, which conducted mostly activities in conjunction with the for-profit vendor, rather than independent advocacy, organization, and education. The subsequent 1983 ruling, 83-164 for a Prime users group, was upheld in District Court in 1987, and similarly on appeal in case with Guide International, an IBM group dating back to 1956 but incorporated in 1970. However, these were all about c6 business societies, not c3 charitable exemptions.
So this is why we set up the Berkeley Macintosh Users Group, started in 1984 as a campus club, legally in 1985ish as BMUG, Inc. (unofficial motto when filing: "No, it doesn't stand for anything") and while applying for 501c3 status and for years afterwards made some mostly-token efforts at cross-platform inclusion, including publishing a Windows newsletter, attending a Comdex, and doing a poorly-named "GUIfest" rather than our traditional MacFest. Of course, its primary relationship was with Apple and over 10,000 Mac users. The nonprofit status turned out not to matter much, as an insubstantial part of the organization's revenue came from donations, and in most cases these were not deducted by the donor.
As the IRS sez (PDF) in a 1996 thoughtful analysis that illuminates some of the type of thinking and precedents that eventually led to the latest ruling:
One problem common to many cases concerning computer-related organizations is language. Computer enthusiasts tend to use a jargon that often does not translate easily into the language of the federal tax laws.
Over the course of the past few decades, I've seen over and over again the pattern of people forming organizations go through all kinds of gyrations to qualify that take energy away from the project itself, or deeply influence the collective sense of what is possible. It behooves every group that wants to be effective to take time in formation and on a regular basis to step back and look at the big picture, to talk to partners and advisors and members and seriously ask the question: "is this organization serving us or should we lay it down and work together in new ways?" If your group isn't meeting members' or the community's needs, people will vote with their feet and/or wallets and energy and attention and you'll end up moving on sooner or later.
I am a fan of Benefit Corps. LLCs, and other new forms that add more flexibility and ease in aligning structure and purpose; they provide new levels of agility and ease in cooperation, for whatever collective purpose.