It is seriously about time! The D-pad on the current controllers is absolutely awful (for those who don't know, often times it registers the wrong direction due to poor mechanical design). It has made some games (especially live-arcade games like megaman 9) incredibly frustrating.

Its naive to think that buses are only good for storage.
1080p video is 1080*1920pixels/frame*32bits/pixel*60frames/second is roughly 4Gb (uncompressed). If history is any indication displays will get larger and denser (also remember bandwidth needed will scale by the square of the number of lines). Or what if you want an external GPU? 16x pci express is about 32Gbits/sec. Also more speed reduces latency, which may be helpful too depending on what you use it for.