In case you missed it, there's been a recent leak which has offered up all kinds of Nintendo stuff, such as early prototypes of famous games. However, information has also been uncovered relating to games which never made it into production, the most exciting of which is a proposed Pokémon MMO from 2004.
The idea was pitched by Chinese company iQue, which worked with Nintendo to create Chinese variants of its systems, amongst other things. While the main game could be played offline on the Game Boy Advance, iQue's proposal would have seen the console getting plugged into a PC for online play, with this element being based on code borrowed from Pokémon Colosseum (the offline mode would apparently have been based on FireRed and LeafGreen).
Regional differences would mean that monster distribution and in-game weather would change depending on where you were in the world, and when you logged on.
A 2005 release was mooted, with online functionality apparently coming a year later, but this of course never happened. We may have seen similar functions in subsequent Pokémon games, but it's fascinating to think that we could have been playing an interconnected Pokémon world as far back as 2006.