While this sounds interesting, I do have questions on organization. Will there be a subreddit devoted to this? How will 'submitters' be organized, if at all? etc.
In order for it to succeed as a 'convention', people have to be able to post their work in a way that their work can be organized, found, and seen by other people within the scope of the convention as well as externally. Additionally, since /r/Touhou would get swamped depending on how many people submit, Reddit's system would immediately root out slightly less popular entries and demote them, resulting in a very unfair balance depending on the time that someone posted.
Just a few concerns.