There have been many discussions about this in the past...

Personally I would think it would be a good thing to do to clean up a few action bar slots... But certain classes couldn't get it done. Monk and Samurai being the most prominent examples because of Perfect Balance and Meikyo Shisui respectively.

There are some other squashing that could be done to save space on some classes other than the combos as well.
PLD, Confiteor needing Requiescat to use, it could easily change into Confiteor upon being used and when it gives the buff... Maybe add a slight internal cooldown between the two to avoid Confiteor going off too early.
WAR, Primal Rend needs Inner Release to use. Simple.
DRG, Mirage Dive can only be used after using (High)Jump.
BRD, Shadowbite is only usable after a proc from Quick Nock/Ladonsbite, Pitch Perfect only usable during Wanderer's Minuet.
MCH, Rook/Queen Overdrive is only usable while the Rook or Queen is active. Heat Blast is only usable during Hypercharge.