I think it's a good idea, although it is a bit of a stretch to decide who's fault it is that the ball was tipped. Saying it is somehow not the QB's fault when it is tipped by a DB but IS the QB's fault when tipped by a defensive lineman, is just too complicated. And the QB is partially at fault in either case, anyway. What if the lineman drops into coverage? What if the DB tips it and then intercepts it?
And to top it all off, if you can figure out a reasonable way to distinguish picks from INT's, the stats for all QB's of today would artificially improve compared to previous QB's. That whole debate would fire up.
It's a good idea, but the mechanics of deciding it would just be too complicated.