I like the sound of that. Really, the one-timers were only limited by if you could get a Ditto and if the Daycare was in the version you were playing.
On that note, are you going to include a breeding center? Thinking about it, it sounds really difficult. But you could probably cannibalize GSC for most of it!
But speaking of one-timers, I'd really like a way to re-obtain things like PP Ups, Nuggets, Max Elixers, etc. because from a collector's perspective, it gives you something to do after you've beaten all the dungeons and battles, when you can do something like go to the end of Cerulean Cave and get another Rare Candy :3