Sadly, I won't be able to do a Dreamcast livestream marathon today, simply because I'm not at home. However if I get time to I will make sure I do one marathon this year, wherever I'll do it on the PAL launch anniversary or the Japanese one I'm not sure yet, but will let you know when I do.
Let's LIVE Videogame. He has a list up of games he owns and intends to play there. There is also going to be a 12 hours marathon over at Cornerb0y's twitch.tv account too, and I am sure there are bound to be others going on over the next day or so (if you are doing one, let us know and we'll edit the link into this post).
Pcwzrd13 did a livestream yesterday, which you can watch a back up of here, if you want your Dreamcast livestream gaming right NOW.
I didn't want to go without doing anything for the anniversary, though, so I do have something for you guys.
Hopefully I'll find a video use for Dee Cee in the near future.