This should probably be a full article with an in-depth look at Nintendo's history, goals, and motivations, but I just can't be arsed to write one at the moment. So here's the cliff notes.
Premise: Many of Nintendo's minigame are Proof of Concept (PoC) tech demos packaged into a collection. By paying attention to the tech demos, it is possible to understand what games might be expanding on those concepts.
Evidence: The cow riding game in Wii Play appears to be the same motions as Excite Truck. The "duck hunt" game in Wii Play proved out the concept of using the Wii Remote as a Zapper, giving us Link's Crossbow Training. Fishing and Billiards also paved the way for more sophisticated titles of those genres. Baseball in Wii Sports gave us Mario Baseball.
E3 Predictions:
- Wave Race (based on the jetski minigame in Wii Sports Resort)
- Red Steel 2 (based on the sword fighting minigame)
- Tiger Woods Golf w/Motion+ (improved putting based on the minigolf minigame)
Granted, two of those are already announced. That only leaves one game as a clear surprise. However, I do think we'll be seeing one more title being announced based on the themes they've shown. I imagine that Resort will also carry a few flight-based games.
Remember the flight-sim demo that Nintendo showed where you could fly the plane with a twist of the wrist? That didn't fly so well (pun intended) because of the control limitations. But if I know Nintendo, they're going to try again with that codebase and use the true 3D spatial positioning of the Wii Motion+ to compensate for the previous control issues. Which points to one other franchise title...
(drumroll please)
- Pilot Wings
There you have it. Those are my predictions. Place yer' bets. 

