I find your idea interesting, I would only suggest that to aim at a 100%-focused keyboard solution, it would be better to consider that "actual monitor = monitor where the window is".
Regardless, and to be honest, I have posted the code for GridMove on github
because I haven't been able to followup on the requests posted to the forum (I've explained it elsewhere, but basically not being a Windows user anymore makes developing GridMove a burden instead of a pleasure).
So, unless someone else steps up to fullfil your request, I fear it won't be done
I'm really sorry for this,