From their website it sounds like "Anything goes" as far as what bikes are allowed.
FWIW I have registered, in the Novice class, natch
Might be interesting to see where the lines are drawn, if indeed they are
The only drawbacks I can see are a) I'm not entirely sure whether I'm actually free that day and b) riding in big groups makes me really,
really nervous, largely as the result of an incident on a club ride longer ago than I care to remember in which I came down in a bunch, whilst riding fixed. I was a bit of a mess ...
Pity there isn't a 'Fat Bastard' class ...
I love the idea of 'urban cyclocross', though.