Indeed that would be interesting. I did try to look up the same for the Belgian competition but failed to do so.
More than probably also there will be a decline.
Which is maybe good. Other sports are getting more practitioner and viewers.
When I was a kid, it was normal than more than 90% of the kids did choice football as sport. Now there is broader spectrum of sports they can choose from.
Still both my kids did (voluntarily) choice football :)