It's reasonable for Nintendo to come out with a new model by 2009. However, if they do, it will not have high definition or other major changes that would cause software incompatibility. Some things possible for a new model that could be released soon include:
Color choices
Built in wired ethernet (instead of having to by a $20 USB adapter) for high performance online play.
Built in hard drive to replace or supplement the built in flash memory
Rechargeable batteries as standard.
Rumble also in the numchuck instead of just the wiimote. How did they miss this in the first design!
Color choices for the glowing led around the drive. Maybe even have different colors mean different things.
The only way I see Nintendo releasing a high definition version of the wii within 5 years of launch, is if the PS3 or some other model starts to outsell the wii. The more and longer the wii dominates sales, the less likely and less different changes will be.
