1. Individuals who want to share replays with friends.
2. Professional teams who want a scalable way of taking video of their players' games and hosting them on their sites.
3. Tournaments that want to host all their games in video format (don't want to distribute replays) but have scalability problems in doing so. They may be tentative about uploading such replays to your site, so a more formal partnership might work better.
4. Individuals who want to "watch replays" on mobile platforms.
5. Individuals who want to "watch replays" on machines that can't handle sc2 (or people who don't own a copy of SC2).
The need for replay watching is somewhat diminished compared to the days of Broodwar, when there was a dearth of videos of games available (nowadays, youtube videos of games are just everywhere). Where you might find success, is with groups who are really keen on watching replays of games that are one of those one in a million kind of games that weren't broadcast for a tournament. (I remember there was one such game -- Sea vs Savior -- during Blizzcon 2008 that was only played backstage and was basically never shown to the public)