I can't see any reason why a 10M race couldn't attract a big field if you had a route that could accommodate it
I think most current 10-milers attract the size of field they're comfortable with
i.e. they limit numbers to what the course will take, don't advertise much, and fill up on word of mouth - e.g. in my neck of the woods (North West) there's Preston, St. Annes, Great Warford, Wagon & Horses (Lancaster), Sale, Snake Lane, Llandudno, Penmaenpool, Caldervale, Derwentwater, Swinton
Brampton To Carlisle and Stockport are probably the two biggest that I know about, and even they limit to 1000 entrants.
I imagine there are plenty of people who've run a 10k, who maybe see the step up to Half-Mara as a bit daunting, would jump at a 10M
it would just need the right emphasis in advertising, which would be easier to achieve for a newly created race
Edited: 07/11/2012 at 17:33