I think you could definitely find people interested in something like that but it may take some time before it gets much in the way of participation. I'm not for sure if there's a community dedicated to dancing but I think it'd catch on much quicker if you could partner that with a community. Lots of times around here it seems like it takes everybody seeing someone else doing something a few times before they catch on and join in.
I say go for it! You don't lose anything by trying and very well may find other people that enjoy it as well.
That's fine but a starting point is to identify the dancers, which will be a bit difficult
True, all I know to do is throw a post up and see what response you get. Maybe mention it for a bit in your other posts and see if you get any positive responses? I tried to start a contest and got zero entrants so I'm by no means an expert on this :)
When you got zero entry what did you do next, would love to know?
I'm still trying to figure that out myself, haven't tried it a second time yet. Will be doing so very soon, will let you know how it turns out.