What would happen if you put your uncooked potatos in a blender and then cooked the result?
Would you get mashed potatos? Faster?
I doubt that most blenders could handle raw potatoes, though a food processor probably could. The problem with your idea is that they'll be easier to cook before they're mashed, and easier to mash after they're cooked. I see no advantage and plenty of potential disadvantages.
I'm with Michael: it sounds disturbing. I think you could probably get away with it though if you rinsed them after blending, and then saute'd them after in a little (probably a lot) of butter.
I think you need to leech out a little starch or heat it enough for it to start breaking down. Traditional mashed potatoes are lighter, having lost a good bit of their starch in the boiling process.
Mashed new potatoes, or mashed baked potatoes, or any other variation on the whole-cooked-potatoes-mashed theme tend to be much more starchy, but this is somewhat alleviated by the flavors imparted by cooking.
I think, if you just shred them and then cook them, you're going to end up with the worst of both worlds: heavy, not especially tasty, potato mash.