From what was released by the media tour, there is a growing concern amongst myself and others about how busy and oGCD heavy the general rotation for GNB will be next expansion. Specifically when it concerns the timings of cooldowns and general movement during raids. Now while we have no idea how movement intense the next raid tier may or may not be, what we do know is we are given a forced oGCD, Hypervelocity, after each Burst Strike, and an increased cartridge capacity meaning more Burst Strike's meaning more Hypervelocity's on top of the already forced oGCDs after your Gnashing Fang combo GCDs every 30sec.
Currently you can utilize Burst Strike as padding to get any double weaves out necessary in time for a mechanic, or to move a boss without clipping your GCD, but a FORCED oGCD that you must use or lose restricts this current form of flexibility. Double Down on the GCD will give us some of that breathing room back, but only once every 60sec instead of the readily available Burst Strike that simply requires a charge. Normally, if you have the timings down, you can pre-pop mitigations necessary for a mechanic, but this only is effective if you are not trying to perhaps contain two damaging mechanics within a mitigation window.
Endwalker also introduces another issue of Heart of Corundum's(HoC) initial duration. In order to get the maximum mitigation of HoC, you must apply it to yourself or an ally within a 4sec window. While PLD and WAR also received similar effects, they are not prone to the cursed amount of forced oGCDs that Endwalker GNB will have, making the timings for HoC harder to accomplish. There is also the extra charge of Aurora which is yet another oGCD we must weave, but that is minor in comparison.
There are other minor issues that may or may not be prevalent by the time of expansion such as the 30sec Excog effect being overwritten by the 25sec cooldown of HoC, No Mercy's duration not long enough to apply to a final Burst Strike's Hypervelocity and not long enough to contain all your bursts strikes, Gnashing combo, and other GCD abilities during a Bloodfest window, etc.
TL;DR Endwalker GNB is about to reach Stormblood DRK levels of oGCD spam. Just wanted to get a non-DRK related Endwalker discussion going about the potential future of GNB.