It's an interesting design problem for sure. Do they make it a USB dongle and have an HDMI cable going out? Or an HDMI dongle with a USB cable going out?
Function-wise two cables would be the better design. On my TV this dongle would probably interfere with cables in the ports next to it. In this picture you can imagine the problem if there was another HDMI port right above the one it's plugged into, https://lh6.ggpht.com/jbhD_qpdQkLDEk4Y6PV9E2vBWM7__xjVzE18_J...
