The new Wiis, which are part of new shipments of the console, have an altered circuit layout that makes modification more difficult than in earlier versions. Users attempting to mod the new consoles using current modchips are very likely to damage the system, the sources pointed out.
Interestingly enough, they aren't actually saying it'll be completely impossible – just much more difficult, and take more time. At least they are being realistic. Is Wii piracy already that much of an issue that only a few months after release they want to attack modchips?