There's no Virtual Console retro games yet, but I think it's a natural move. I'm really surprised they didn't announce the retro downloads at E3 this year. Right now, it's only new titles. And there's not that many of them. And they're not very good necessarily...
I never owned a DS system, but I got into the DSi for the main reason that I believed they were heading this way. I wonder though if there's some kind of transition they need to make from the old LCD graphics of the original GameBoy to newer screens.
I'm not a techie in this regard by any means, but original GameBoy titles might be excluded because they relied on the screen's natural green colour for some background elements. So, they may only be able to port over remakes like the colour version, but originals might be unavailable without some tooling around. Just a thought.
(Is it true that you first must register your Wii before you can start using Virtual Console? Why? How do I find the "registration number"?).
Check out
http://www.nintendowifi.com/ for more info. There's tutorials and step-by-step walkthroughs. It's not as hard as it seems. I do warn you though, it's highly addicting to get starting in downloading all those retro games. They do come cheap though, roughly $5 to $10 a game, so it's not so bad!