Does the fact that it's not finished matter? Can this be fixed by officially extracting its part as a "first volume"?
If you do call it a "first volume," make sure to put the cutoff right after Ch. 63 "TSPE Aftermaths" if possible. It'll make more sense that way because its the end of an arc.
This year I'm a supporting member of WorldCon for the first time, and I noticed that the Hugo's have a category for Best Fan Writer ("Any person whose writing has appeared in semiprozines or fanzines or in generally available electronic media during 2010."). I do believe Harry Potter and the Methods of Rationality counts, and I plan on nominating it. Even making it onto the ballot will probably expose it to a wider audience. Is anyone else here a WorldCon member and thinking of nominating MoR?