Surely the measure of the GPL3's success is how well it has achieved its stated goal of protecting the freedom of computer users who use a particular program, and by extension the FSF's broader goal of freedom for computer users generally. On that measurement the record is mixed. The new licence doesn't seem to have helped at all against what we used to call 'Tivoization' - locked-down hardware on which you cannot install your own programs or make changes to those installed. In most cases where the new licence might have made a difference (for better or worse), most free software authors have chosen not to adopt it. There isn't a critical mass of GPL3-only software which might make hardware vendors think twice about shipping locked-down hardware and so excluding the use of GPL3 code on it.