Every now and then a really new thing comes along, and Plan 9 is one of those things. It's been quietly waiting in the wings for its moment to shine. There are days I wished that Plan 9 had been released as GNU licensed open source back in the days when Linux first got going, or something more along the lines of QnX, lots of things are unnecessarily hard the way they are now.
We (the Plan 9 community) figure that not initially releasing it as open source cost us Linux's current place. As it stands, we didn't open source until 2000.
But we wouldn't have put it under the GNU license in any circumstances, we have grievances against GNU :)