SB,
They already do.
Most new maxis have the lead on a keel that can be swung side to side by hydraulics. However, racing rules require a certain amount of stability with the bulb hard over - otherwise an unintential gybe or round up could be nasty. The biggest problem with this system is building it strong but light enough - one failed spectacularly on the Sydney to Hobart a couple of years - actuating arms broke, keel swang violently from side to side until it departed the yacht.
Most yachts with this system do have a controlable foil close to the keel in addition to the rudder.
Like aircraft, weight is critical in racing yachts. A certain amount of ballast is always required in monohulls, and the longer the moment arm you can attach it to the more righting moment you achieve. More righting moment allows you to carry more sail area, and to point higher into the wind.