If I had to guess:
Pokemon: 6th generation comes out in 2013/2014, around the middle of the 3DS's lifespan. This guess is due to the fact that there are usually three years between games, and 5th gen is already out in Japan and will be released elsewhere around March. If the 3DS has a similar lifetime to the DS, this will be somewhere in the middle of its life.
A Mystery Dungeon game will come out in 2011 or 2012. Those games have sold well enough in the past, and the last game was released about a year ago.
A pinball game, like on the GBC and GBA, is not out of the question, considering the prescence of a Metroid pinball game on the DS. It just depends on what they want to brand it as. Such a game would come out relatively early in the 3DS's life.
A game along the lines of "Hey You Pikachu" is unlikely, considering the fact that Nintendo already has Nintendogs.
Pokemon Ranger games, similar to the Mystery Dungeon games, come out every 2 years, so the fourth entry in that series will probably come out 2012.
I severely doubt that Pokemon Grey will be a 3DS game. Remember, Yellow came out around the same time as the GBC. I expect Grey to be the last great DS game ever made.