I think it's an awesome idea if a) you have the room width and b) you have one of the new/bigger front loaders. Those machines stick out so far that you will make them look way more proportional to have a deeper countertop. Just make sure your sink is installed toward the front of the cab so it's ergonomically correct for you standing at it.

I have a cabinet for a double oven that we added shelves to in my laundry room. It is the same depth as my w/d plus room behind them for cords, etc. I love it because I have all my detergents in the top section and the bottom is wide/deep enough for laundry baskets. I hated the way my old cabinets weren't the same size. It looks so much more intentional now.