Only items that are currently available in Route would be obtainable for this item drop, the same way that only eggs for Pokemon currently available in Route can be procured through it. That way, players are welcome to use the drop as a means of getting hold of an in-game item that their character might not have the IC motive or ability to otherwise - either because it's too expensive, or they'd have to travel a long way to obtain a wild Pokemon they'd otherwise want, or something like that.

If there's an in-game item you'd like your characters to obtain, feel free to ask us about it! Otherwise, you'll unfortunately have to come up with a different idea, sorry.