Yea I could see Kia doing a higher end coupe, but it should be its own thing, not just a coupe version of the K900. It could use a bit of the styling from the K900 though. It is stiff competition in the luxury coupe segment though, so they would really have to pull out all the stops.
They could craft themselves a competitor to E-class coupe and 6 series. Both of those are relatively low volume, but if KIA wants us to take them serious as a luxury brand they need to come out with 4500 model derivatives just like BMW and Mercedes.