A picture from a Minna no Pokémon Bokujō (My Pokémon Ranch) flyer released on the Japanese Imageboard 2ch has some more information about the upcoming Pocket Monsters Platinum compatibility.

According to the official Minna no Pokémon Bokujō website, the update will be available some time in November. Those that have the game already will be able to download the update for free when it's available. Those that don't own the current version will be able to download the updated version as well for 1000 Wii point.

The update will increase the number of Pokemon that can be stored in the farm from 1000 to 1500. The picture also indicates that Giratina's Origin Forme with be depositiable and Shaymin Sky Forme is also compatible with the new update. With the recent announcement of Rotom's new formes, it is most likely they will be included in this update as well.