While there is no doubt of a culling i think there is another way to free up button space.

auto forwarding combo buttons, proc based skill changing buttons, stat based skill changing buttons.

And before the "but this will make the game dull end easy" crowd jumps in, we allready have them ingame outside of PvP.
WAR: Fellcleave/Inner Beast, Decimate/Steel Cyclone;
AST: Draw/Play Card, Spread/play Card;
MNK: Tackles;
DRG: Geirskogul/Nastrond;
NIN: Ninjutsu;
SAM: Iaijutsu;
MCH: normal Shots/Heated Shots;
SMN Ruin II/Ruin IV
These are all ingame and some of them were ingame before the PvP button culling.