Well to start off with, 24 hour race already is a very tough race to finish, so 24 hours would be enough IMO.
Next off, the idea is great and surely the idea has been running around most racers heads every now and then, and sure it is achievable thing to do, but then again, interest to LFS is rather small nowadays and tbh I don't see anything like this happening before S3 comes out, some proper advertising of the game + event have been done. So, well, before the interest of 250-300 participants (including racers, streamers, organisers, marshals) I wouldn't start planning anything bigger as of now. Remember that LFS racers are spread all over the world. Many, many people will struggle to get there. If you have 3-4 teams at this LAN event and rest 24 teams thru internet, I don't see this thing happening.
But like I said, it's a good idea and could be worked on.