From eurogamer.net:
Microsoft's Kinect team is said to be working "very hard" on a switching or compression technology that will allow a greater amount of data to pass through Kinect to the Xbox 360 console.

The depth sensor used by Kinect is also dictated by firmware – it is currently set at a 30 frames per second limit and a 320x240 resolution limit. At a 640x480 resolution, however, Kinect could begin to detect fingers and hand rotation – an effective quadrupling of its accuracy.

The issue relates to the USB controller interface, Eurogamer was told. It is capable of around 35MB/s, but it only uses around 15/16MB/s. This artificial limit is in place because multiple USB devices can be used at once on an Xbox 360.
There probably would not be an issue with Slims, as the Kinect has it's own plug, if it is on it's own USB controller. It's the other models, that have three on one hub. Still, the Kinect uses YOU as the controller, and even with a WiFi adapter plugged in to the one rear slot, should not use more bandwidth than required for the upgrade.