I just know GIVI will not give up the opportunity to make a box fit on the grom. It wouldn't be long till they come up with the proper brackets to make it fit, it's just a matter of getting their hands on a Grom.Backpack sir!
I wonder if Givi will jump on board for the Grom. They make racks for other Hondas. I have a vfr800 with Givi racks and side bags. Don't know how i ever rode without them before XD they are very useful.