What would happen with jobs such as monk, samurai and ninja who get skill speed buffs/straight reduction of their gcd speed? Is it a straight .5 off or does it scale for longer gcd skills like fire 3/blizz 3/ flare? Would it effect a machinists heat blast which is at a fixed 1.5 gcd or would it further reduce it?

Combat would change significantly for a number of jobs, some of which don’t even want skill speed or spell speed to reduce their gcd, anytime you got sync’d to a dungeon at or below 50. I personally feel a change like this would cause more harm than good because you’re getting used to that faster gcd just to have to “slow down” when you get to 51+.