I don't believe its exclusive to GW. All it is is a SDI Tech which all characters can do from the air. It's just being applied to one of GW's more reliable approaching options which is his Bair and using it as a possible counter to DS OoS.
Even Marth can do it when he expects to get hit while in the air close to the ground, which leads to the following counter possibility:
GW Bair's Marth's shield
Marth does a DS OoS
GW SDI's the DS into the grounded and techs it to recover quickly.
Marth is in the air after DS and FFs.
GW runs in and attempts to Usmash Marth.
Marth does the same thing and SDI's the Usmash into the ground and techs it.
Marth counter attacks the now grounded GW.
The turtle vs shield situation still ends up in marth's favor because for this to work Marth needs to DS OoS shield GW is in the air. Marth could just use the 5 frame startup/invincibility on DS and activate it a couple frames before GW lands, causing him to eat the DS while in his landing lag. If he does manage to get the tech off then whatever he plans to counter with will be telegraphed, usmash fsmash aerial etc. so the marth though vulnerable has time to pull the same tech out on him.
