There is also a Scorpion version of the AXG.
In Sigs video, Phil Strader mentioned that the AXG grip module (not the Scorpion version) will be offered as a standalone grip when you go to their fire control website. So as sam4886 said, you can buy the FCU and pick up whatever parts you want, Sig or 3rd party, versus buying the whole gun just to get the AXG grip. Though nothing wrong with buying and owning multiple P320's.
Bonus announcement is the new XFL magazines.