It's interesting that this has happened; it makes me wonder how they intend to keep their competitive advantage because that's historically been the reason for keeping the drivers closed, so that it takes much more time/effort for the rivals to pick them apart and figure out how to make better gear.
Then again this also presumes that nVidia's drivers will be any better; yes, there's been closed drivers as blobs for years, and many people didn't particularly care about the open source part of it - there's a lot more pragmatists than ideologues in the Linux world (though there are many more ideologues in the FOSS world than there are in the Windows world for sure), for whom openness is a nice to have rather than a requirement. But my memory of nVidia's Linux drivers is that they were all pretty rubbish anyway, closed or not.