Photos of Luxury package RX models show an extra switch on the side toward the front. This is the furthest forward switch. Is it for extension of the seat cushion or what?

 

Yes, it's the thigh support extender. If equipped, both the driver's and passenger's seats will come with the extender.

Taller people with longer legs may not find it too useful since it doesn't extend that far out, but your mileage may vary.

 

At 5'5 I love the extenders

 

Although the extender doesn't appear to move very far, for me, it makes all the difference in supporting my legs and taking the strain off my lower back. My feeling is that if you drive with your seatback somewhat reclined the thigh extenders make a bigger difference. If you sit more upright, you may not notice the effect.

 

At 6'1, they didn't do much for me