This is a really cool idea that allows for something the site can't really have otherwise- pure-dialogue, short-form writing, which provides a whole slew of crunchy challenges to sink your writing teeth into. Forcing people to tell a story through just characters speaking, with no room for fancy prose or highly conceptual ideas, will no doubt lead to some really interesting little stories.
Learn to dialogue, people, or I will materialise in your walls with a typewriter and force you to dialogue on it until you can convey eight hundred years of worldbuilding and every emotion and sensation known to humankind through a short conversation about the weather