That's not exactly the wallhack fix I had in mind, and I'm not sure it would actually do the job of nerfing the ability enough. For instance, it's easier to have the minimap ability function based on overall movement speed since it only registers things as a dot, but if it's part of his vision, what would happen if someone moved one finger faster than 2mph? Or what if their heart beat moved those muscles faster than 2 mph? (which I'm pretty sure it does) It would defeat the entire point of having the limitation in the first place if he can see any object/portion of an object moving faster than 2 mph.

Edit for Drall: Mach 1 should be fine, since he can summon dozens of spikes at once and fire them in whatever pattern he wants, making them innately difficult to dodge.