Not only it comes in a booming segment...
...but it will allow Lexus to grow the RX, to better compete with the X5 and ML, rather than having it to balance between the X3 and X5, and maybe to give it a 7 seats version like dealers want. There are also rumors talking about Lexus working on CLS and X6/X4 rivals.
Not sure if just following the niches set by the Germans is a smart move. Lexus should create its own niches, and wait for the Germans to follow.