Wait for Wii ware. I put renders on my DLP all the time with it! But Wii ware may let you do more... Oyeah there is no way in hell you are going to get away with modding when these systems are online.
Don't wait for Wii Ware. All you can do with an SD card is save, watch you pics, and listen to your mp3's. You will never play anything off the SD card because Nintendo said that it's too slow. Nintendo just needs to come out with a hard drive that connects through a USB cable.