If I'm the first to discover this, I want to call it GBG Cancels!
TL:DR - There is a lot to talk about in this video but for now enjoy a quick demonstration of the type of Dive Kick cancels you can do. There are two ways to perform this: the first method is to time your attack right as the move connects and you get an visual impact and perform your grounded/on-ground option, the 2nd is to perform the dive kick extremely close to the ground where it "Land-Cancels" and you can perform your grounded option. Both methods are very strict.
Long Read because I don't have a proper recording setup:
This is speculation and needs more testing but when you do a Dive Kick there are a few frames where you are considered "grounded" so you are able to perform other grounded options, so if you ever wondered why the Dick Kick (DK) felt a little weird this is one of the reasons. In the video I demonstrate what the normal DK is and how you can cancel it into grounded options:
1st Demonstration: is the normal Dive Kick and what happens when you whiff (Miss)it
2nd: DK hit confirm and its regular push back
3rd: DK canceled into Grounded Normal Attack
4th: DK canceled into Aerial (Grounded) Dodge
5th: DK Whiff(Missed) into low aerial focus heavy attack
6th: DK Cancel into Jump (this cancels out the push back so you can cancel into grounded normals or special moves)
7th: DK whiff cancel into grounded normal attack (Removes all landing lag from missed dive kick)
This is just the start of the Dive Kick cancels. DK can be canceled into Spirit Summons, Vessels, Spells and probably every other thing that can be done on the ground. The best DK cancel-Vessel I found so far is DK cancel into Wind Tamer Vessel which causes massive stun and stagger. Its funny how Dive Kicks continue to be broken in non-fighting games. I hope this was possibly intentional and the developers don't remove it from the game since it expands some of the combat system. I hope in the future they could possibly widen the window to perform the cancel.