It seems it won’t happen due to the default keybindings:
We now use a spatial model where horizontal shortcuts/gestures (super+alt+left/right, 3-finger swipe) navigate between workspaces, and vertical shortcuts/gestures shift between session ↔ window picker ↔ app grid. That is, we already use both axis for navigation, which is incompatible with a grid workspace layout.
I don’t understand why a different keybinding cannot be set for “session ↔ window picker ↔ app grid” to implement this feature. I personally use a hot corner for window picker and the Super key for the app menu.