While I had no evidence, I have suspected for months that one of the reasons why Nintendo was moving towards the Wii U tablet approach was because they had decades worth of (pretty decent) game prototypes involving handheld-console connectivity that were unmarketable.

Some of these prototypes would have found their way into Nintendoland, but they could easily have multiple "Nintendolands" worth of prototypes many of which could be expanded into their own game with how long Nintendo has produced handhelds and home consoles.

If you could get it set up Zelda Four Swords Adventure was fun

He might be referring to realizing the under-utilized potential of the GBA Cable through today's Gamepad instead.  I had Pac-Man Vs. and would play it in groups of 4 people.  I played as Pac-Man with a view of the entire maze on my GBA.  While 3 of my friends played as the ghosts with limited "bubble" views of the maze.  As Pac-Man you had the advantage of seeing where all of the ghosts were in the maze and you could plan routes to avoid them.  As the ghost, you had a very small field of vision, forcing you to blindly run around the maze until Pac-Man came within your field of vision at which point you'd have stay with him to chase him town.  The three players playing the ghosts would bark directions to each other as they tried to track down and trap Pac-Man.  So, there you had 4 people all playing the same game simultaneously but having a very different experience from the main player.  Everyone I played it with had a great blast, and I thought it was an extremely innovative concept at the time.  What I think he is referring to, is bringing that concept back with the Wii U in that more than one person would be playing the same game, but the players with the Wii-motes focusing on the TV screen would be having a different experience than the player focused on the Gamepad.

wow sounds interesting. i gusse it's a good idea. very interesting concept. who wouldn't want to play as one of the ghost?

He is NOT talking about connecting the 3DS with the Wii U. He is talking about using the screen on the Wii U controller as the GBA was used when connected with the Gamecube. Connecting the 3DS and Wii U would just cause all the same problems as before. There is a reason the second screen is included in the box this time.

As a side note, Pac-Man Vs. is the most fun I have ever had with a local multiplayer game.