Beside what borkymcfood said about the gluey part, I wouldn't go around increasing the surface area of the potatoes before cooking them for mash.
Whole boiled potatoes are thirsty. When you cook them whole, the starch stays much less hydrated than when they are cut up in small pieces. Then you use a ricer to break them apart while hot (which is easy at that point, the cell walls separate of their own accord) and add the milk. The milk binds well with the starch, and makes a nice cohesive texture.
You can get away with cubed potatoes too, but not as well as with whole ones. But if you shred them first, they might get soggy. I am not entirely sure if this will be the case if you make them in a sealed bag, but there will be juice getting out of the vacuoles, and it might be enough to make them waterlogged in the bag. If you cook shredded potatoes directly in water, they will go soggy for sure. And soggy potatoes do not make smooth, nice mash.
In the end, people rice potatoes because it works. Depending on how frequently you make them, you can decide if you want to invest in a more complex hinged ricer, to stay with a simple stamping one, or just use a fork. You will still get better mash with less effort than cubing or shredding, then doing sous vide, then trying to puree them without blunt force.
