If it can be restricted, it is.
Play-Asia recently received their shipment of Japanese Wii units and took some time to test out region lockout on Japanese and US systems. Unlike the Nintendo DS, Japanese Wii systems only support the Japanese language. Play-Asia tried booting a US Wii disc on a Japanese system and vice-versa, but neither worked. They also tried using a Japanese Wii Points card on the US Wii Shop, but the number was rejected as being from the wrong region.
Datel's Action Replay and Freeloader discs do work on Wii, so import GameCube games can still be played. However, there does seem to be some trouble loading certain games and using certain memory cards. I also tested the unlicensed Game Boy Advance game player, Advance Game Port, and found that it had to be booted by Freeloader in order to load. On top of that, sound plays at 1.5 times normal speed, likely due to the difference in clock speed between the Wii and GameCube.
As for accessories, they are not region-restricted, and work on systems from either region. However, those hoping to play import Wii games will either need to import a system as well or hope for a Freeloader-like solution to surface.
