I think the actual reason this key is in Dolphin boils down to a historical accident of how game dumping and piracy used to work immediately after the Wii's rel

I think the actual reason this key is in Dolphin boils down to a historical accident of how game dumping and piracy used to work immediately after the Wii's release. Originally, people dumped games using certain DVD drives that were capable of reading the non-standard Wii disc format using undocumented debug commands, burned them to DVDs, and used modchips to make the burned DVDs look like original discs. (This is long obsolete and replaced by softmods that can just rip and run games on USB drives or SD cards using software running on the Wii.) People doing this had no way to decrypt the data and no reason to since the Wii expected it to be encrypted. So in order to be compatible with game rips designed to run on the Wii, Dolphin needs a copy of the common key. That is, the reason this key is in Dolphin in the first place is - ironically - most likely because it was completely ineffective at preventing game copying.