We don't have any firm figures on the RX400h yet but on the subject of fuel economy, you will only get 23mpg in real life in an X5d, I know, I had a demo when I worked with BMW!
The RX is currently the most fuel efficient petrol SUV in the UK and the RX400h will be the most fuel-efficient SUV full stop.
The acceleration will compete with V8 SUV’s X5 4.4i and ML500, in real life you can expect 18-20 mpg from them. I would expect the RX400h to be almost double! Now that’s a result!
The fact is, Lexus have the flexabilty to tune the car the way they want and we will only know for sure when they tell us and I will probably find out here :)
On the design, there is now a dedicated Lexus design team, the GS is a result of this and I would expect more of a family feel in future models. The last thing I would want is the S Class/ C Class thing where unless you are in the trade, you can’t tell the difference. Good if you have a C, bad if you are in an S!