Ultimately, we've just decided that having unstealable items doesn't make sense. Even magical items - like Confutatis' armor which was infused into her skin - could be stolen, because as it is, only things like magic and a companion bond are an intrinsic/inherent part of your character. Everything else is quite literally an accessory/is external.
We also realize that part of the motivation for unstealable items is, "Yeah but, I don't want this to be taken :( :( :( :(" but that's sort of a necessary evil/fun of the game. Maybe you disagree, but it is something that we've talked about at length multiple times. If this isn't a good enough explanation/justification, let me know and I can elaborate!
As for the tracing magic Neo, Blu has brought that one up a bunch too. But it's PP/MP any way that you look at it, unfortunately.