So yeah, this has been done...
It was done by itsPersonnal and I. We got together, and took turns. It was done over the course of 2 days, but the game and timer were paused overnight, and resumed the next day. So, I guess it's not exactly Single-Segment, but whatever. The entire run was streamed here: http://www.twitch.tv/itspersonnaltoo
Considering this was the first run, we've learned a lot from it, because we got completely lost when it came to Chao raising, but for next time the idea will be to have a really crappy hero and dark Chao just to unlock the races, and have a neutral Chao to actually use. To be honest, proper Chao raising could probably save about 2 hours off of this... Anyway, our guess is that this could be taken down to about 15-16 hours Real-Time/~13 Game-Time, due to many stupid mistakes and levels that we haven't practiced getting A ranks on (Sand Ocean M4, Mission Street M1 during Hero Story).
I'd even go so far as to say that I'd be interested in racing this category (call me crazy), and hopefully this gets more people interested in this.
aaaaaaaaaand, if I stream a run, it'll be here:http://www.twitch.tv/ptorflaxendrosis