Whether or not it's feasible depends entirely on the metallurgical requirements of the piston in question. This is a constant for any stressed metal part. If you can meet the structural needs via 3D printing, then you can do it. I would have my doubts that an application that requires a lightweight forging can be met with a printed metal piece. But, if a sand-cast or die-cast piston can provide the necessary qualities, then a 3D printed one might do the trick. It will always boil down to the actual structural stresses and requirements.