This is exactly what I said -
the player asking the GM. If that's what you mean by player-driven, well fair enough. But to me that's still GM-driven: the GM is deciding and curating the content of the shared fiction.
You also refer to a
lengthy investigation. You don't actually say how that would be resolved in play, but I get the strong impression that it is to be resolved by a whole lot of further
askings of the GM by the player.
I chose this particular example because it is something that
I've actually done in play, using Burning Wheel as the system and Circles as the mechanic for resolving the action declaration
I hope to meet my brother.
This sort of contrast between D&D and some other systems is why I think, when it comes to D&D (or at least 5e D&D), a discussion of best practices would begin by advising the GM that they need to have a good chunk of fiction ready to go. Because the game has no processes for introducing new elements into the fiction other than the GM doing it.