I'm sure the Wii 2 will be HD-compatible.
It would be great if Wii and even GameCube Discs are supported, so you can sell your old systems and the price of the new system will be narrowed.
However, I'm afraid the new console WILL be expensive because Nintendo has to keep pace with the technology of Sony and Microsoft.
The 3DS is also very expensive, so I'm sure the new console will cost up to twice as much.