I doubt the 3500 is going to be WiFi. I think it is just going to be the MX-3000/MSC-400 combo, only upgraded so that the MX-400 (MX-500?) can send back information and the MX-3500 can receive it. It will probably be using the same RF as before.

However, I have nothing with which to substantiate it except a thread from a few months ago that someone posted saying they saw a reference to the MX-500 somewhere deep in the MX-400 Editor. That leads me to believe that the MX-500 is the 2-way RF box that will work with the MX-3500, but that also leads me to believe that it will be based on the MX-400 which is RF.