I would estimate about 90% of the time when someone likes a floor plan they always ask where is the washer/dryer? If the plan does not show it, chances are it can not be modified to fit one.
How important is it to have a washer/dryer inside the unit? Remember you are restricted to under 400 sq ft. A washer/dryer cabinet eliminates valuable storage space inside. So if it is a must, then concentrate only on those plans that have been engineered to include a washer/dryer cabinet.