Fanaelialae
Legend
I don't have a problem with players making up NPCs or places (for example, as part of their background). I'm glad when they do it, since it's something to hook on to that they're invested in.But, even then, no one is saying that the DM can never prepare anything. So, none of these scenarios are impossible. The DM can still do stuff too. It's just that, in my proposed method, the DM isn't doing 99% of the work.
Let's say, though, that one of the players proposed the crown prince scenario. And as part of that, the player introduced the sister that was a 7th level illusionist. Remember, the DM is SUPPOSED to change stuff. So, wouldn't the simplest solution be to use that scenario but change who the illusionist is? Or, hey, even more interestingly, add a second illusionist that is the actual culprit? So, now the party is chasing down the sister, who is being framed for framing the prince. Layers of the onion to peel back.
It doesn't seem to me to be too much work to keep things interesting. You've got the stat block of a 7th level illusionist already since the player gave you one. Change up a couple of spells, and poof, now you have two. Several sessions worth of prep all done for you.
That said, I don't really see the benefit to what you're describing. I could go on the internet and get an adventure or NPC with less effort than assigning "homework" to the players. With the added benefit that there's a very high chance that it will be something the players haven't read and will therefore be able to explore without having to suspend their disbelief. Either way, I still have to analyze the material, and make any desired adjustments. I just don't see how this would save me work. I don't even usually run modules since in the time it takes me to prepare one module, I can come up with multiple adventures for personal use.