Don't know when this happened, but seems to have been developing for the past few months. Checked about a month ago, and found information only about stuff called SNEEK and UNEEK and whatnot. The steps for these were a little complex, and even somewhat concerning regarding messing something up. However, new advances have been made, and now we're loading GC games from the SD slot on the Wii. USB loading still is apparently not possible, with no hints of it happening anytime soon if at all, so we might be stuck with SD for the GC portion.
Here's the guide:
Easy tutorialThere are some issues with extracting ISOs that I've found, and no real way to get around it other than downloading the offending ISOs. CleanRip does a decent job, but has a problem with a few games, at least for me. It wouldn't extract Mario Party 5 and LoZ: Ocarina of Time/Master Quest combo, so I've resorted to procuring them from the webs. There are simply not very many extractors out there, and nearly all PC drives (save for a few LGs) can't read GC discs. I've searched for a few hours trying to get them to work, but none do correctly.
In addition, some require a disc to be in the drive, such as Metroid Prime (yes, it's released on the Wii, but they've removed most of the sequence breaking opportunities). There is also an option to save game progress to the SD card, but not all games quite work using that, so you'll need an actual memory card. Check the compatibility list for all the nuances. Most games work pretty dang well, and many even work when shrunk, which is an option if you need or want it.
Finally, you'll need a fast SD card. The guy suggests the highest, which is a class 10, but I've got a class 6, and it seems to work pretty well on the one game I've tried.