If I were you, I would do a real calculation on the cost and benefit of the KNX vs PLC especially in a new building.
One think that really keeps the costs for a LinuxMCE KNX install down, is the absence of room controllers. You still have the KNX switches if you want, to keep the system running when the PC is dead.
You will end up with around 50EUR per room for the switch, plus around 25-30EUR per light circuit, 35EUR for each blinds circuit. The system devices (IP/KNX gate plus KNX PSU) will run around 250-260EUR. Cabling is around 35ct per meter.
You will save on wiring costs (and complexity), and you are open to the future, for whatever kind of need might arise. And you have a proven, fast and reliable system.