Why did Krastorio 2 become incompatible?
In total, you need to add a few lines as the mod becomes fully operational with Krastorio 2.

if mods["Krastorio2"] then
data.raw["equipment-grid"]["car-equipment-grid"].equipment_categories = {"universal-equipment", "vehicle-equipment", "vehicle-motor", "vehicle-robot-interaction-equipment"}
data.raw["equipment-grid"]["tank-equipment-grid"].equipment_categories = {"universal-equipment", "vehicle-equipment", "vehicle-motor", "vehicle-robot-interaction-equipment"}
data.raw["equipment-grid"]["loco-equipment-grid"].equipment_categories = {"universal-equipment", "vehicle-equipment", "vehicle-motor", "vehicle-robot-interaction-equipment"}
data.raw["equipment-grid"]["wagon-equipment-grid"].equipment_categories = {"universal-equipment", "vehicle-equipment"}
data.raw["equipment-grid"]["artillery-wagon-equipment-grid"].equipment_categories = {"universal-equipment", "vehicle-equipment"}
end

Circular dependency.
To make Vehicle Grid compatible I'd have to add Krastorio2 as dependency, but since K2 has vtk plating as dependency and vtk plating needs Vehicle grid as dependency it will produce a nasty error when all 3 mods are present.

K2 already adds grids by itself, albeit not as well as this mod. Flagging K2 incompatible was the easiest fix.

It looks like K2 no longer has vtk plating as a dependency. Would that make these now compatible if the incompatibility flag was removed?

K2 just changed vtk to hidden optional dependency.