Here is what I *THINK* the scoop is on this.
If you go to
www.terk.com you will see that Terk is coming out with a Toyota OEM XM Direct Box. My guess is that this is the part thats coming out in March that will allow you to add XM to "Sat" ready Toyota OEM radios.
The RDS one for the people without a sat button is probably coming out at the same time. I'm waiting for that one so I don't have to use my Myfi in the car anymore. Not a fan of wires and stuff hanging around.