I don't think we can assume that games downloaded to the SD card can be played directly from the SD card. I hope that is the case, but there may be anti-piracy reasons why they won't want to allow games to be played off SD cards.
If Nintendo doesn't announce High Capacity SD Card support and the ability to play games directly from SD cards, I'm not interested in WiiWare & VC titles. I'll stay with the PSN and XBLA where I don't have to juggle media to play what I want. I'm sorry but Nintendo seems to think its still the 80s and juggling floppy discs is cool.