Thanks for the tags. By cardio/running, I meant that running is the most common type of cardio that people do, but by all means, it is open to all types of cardio.
Walking Beast - You make a good point, yet remember, 'if you build it, they will come.'
Discussions on such a cardio board could be:
1 - Best types of training shoes
2 - Regional running clubs and race discussions
3 - Monthly training journals
4 - PR bragging for 1 mile, 3 mile, 400s, 10ks, half marathons, marathons
5 - technical discussions of techinque for rowing
6 - comparisons of the best types of road bikes and trail bikes
7 - who makes the best GPS/HRM hardware
The board could also attract sponsors who specialize in cardio type activities.