OK, I think I get the concept. I've seen some forums where they have built-in random number generators for different purposes, but I didn't connect the dots to forum RPGs. As long as a GM is available enough to set difficulty levels for certain tasks, then that's one way to somewhat automate things. Of course, common tasks could have predetermined difficulty classes. You could also do away with DCs altogether using a system similar to FUDGE or the Vampire system you described.

One idea to implement this would be to have a "Roll Dice" tag, which when the post is submitted, would generate random number(s) for each tag placed in the post to determine success or failure, along with some special markup or some other mechanism to discourage shenanigans.