That is a horrible idea. Fortunately Roku does not have the horsepower for Skype nor does it have an audio input and using the USB port, which does not exist on most Rokus, is, at best, a foolish idea.
While Roku is a versatile little box it is not an all in one device.
There are standalone Skype devices and Skype works well on full computers but making Roku a Skype client would be like converting a Pinto to be a platform for a backhoe. It might work but there are much better alternatives that require less work to implement.
Oh, I agree that it doesn't have the horsepower to transcode.
But I'd love for this to be a feature in the next Roku. Making video calls on my TV in my living room -- that's convenience. It would be a whole lot nicer than having my family huddle around my laptop when we're calling my family out of state.
If the hardware COULD handle this sort of thing I'd be all for it . But it can't.
Do we know that for a fact? SkypeHD compatiable webcams all have integrated encoders, so the roku would not need to encode the stream. That is how they are able to run on TVs that aren't that powerful either. It would need to simultaneously upload the stream while downloading another stream, but that is not necessarily something that would be outside of the capabilties of the hardware. Likely outside of the capabilities of the current SDK though.