Just looking at the caliber of other projects that have gone this way (at the top of my head: Apache, Drupal, Django, Zope...) and looking at Boostrap I don't think it's even close to the userbase/clout needed to pull this off. Even the maintainers of those other projects, successful as they are, tend to have a day job.
I don't know, maybe I'm reading too much into this, but I think it might be a little to early to make this move. Just my 2c.
What do you mean by "not mainstream enough?" Organizations on Github are simply a convenient place to put one or more projects that are collectively worked on by a group of individuals and do not necessarily have a single core maintainer.
Did I make myself a bit clearer? :)
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