I'm one of the old contributors: years ago I did the port from PHP4 to PHP5.
To be honest I can't recall if my contribution was done under GPLv2 or GPLv3 (or if it included the "or later" option), but I guess it was GPLv2+ as GPLv3 was yet to come. In any case why restrict the license to GPLv3+ that is incompatible with GPLv2 while the current license is compatible with both GPLv3 and GPLv2? Is there any strategic advantage for users' freedom I miss? If not, I think that the php-mode would benefit to stay GPLv2+. Giacomo