That's a good idea since I heard that if you fill up that 512mb internal, it will brick the Wii. Also there's a mod chip coming out that's going to allow people to run software from an external hard drive.
i just updated my wii, you can view and select the games on the SD card, but it has to load to the internal HD once you click it. So, it's like a CD loading screen, and I sure Nintendo does a check to verify that the data is legit. Tho, I have nothing against homebrews.