Are there any previous examples of these rpgs?
Last year, the jam was structured around making a tiny RPG, so this is the first year we're trying something like this.
I would recommend checking out some smaller RPGs as they likely embody the kind of material that could be generated in 48 hours.
Some examples:
That being said, don't let these examples limit you (or intimidate you)! If you think you can achieve something bigger (or smaller) go for it!