I believe that the character on the cover may be the Extra boss. For the past 4 games all of the final bosses have been extremely bulky (in clothing, of course :V), but this one seems somewhat... skinny. It could be Kyouko, since that "wavy scythe"-thing is actually part of the cover. It's wayyy to big to be a weapon... (unless ZUN is now going to give all his new touhous ridiculously large weapons. Memes ahoy!)
Oh, and will there be Last Words? I kinda just realized that there weren't any Last Spells in the demo, unlike IN.
Oh, and obligatory GET HYPE comment!