I don't think there's a problem with multiple people doing MTC showcases. After all, StereoGang's video shows the top 5 maps as opposed to only the top 3, and the couple of showcases I made for the past couple of MTCs showed all maps (as well as all offline replays). Everyone has their own way of making their video special, so I don't see any reason to arbitrarily restrict these kinds of videos to only one videomaker.