If Lexus makes the GS a slightly downmarket sedan version of the LC, the same concept-car styling in sedan/liftback form. That's the only way that the GS will be differentiated from the ES.
I really hope this is the case, a 4 door LC sounds like a perfect solution. Can we expect a prototype on the road really soon? I recall there's one article saying the development of the new GS was secretly planned under the code 300b but since then no one has ever brought it up again