You could start by looking at yearling sales figures and track closures/racing date reductions/field size reductions. That would be where I would start gathering my data if I were doing such a project.
I'm sure other people can give you anecdotes, but I think Google will be one of your best friends for stories/stats.
ditto what Epona said but also talking/searching the breeding side of things. Most stud fees have been reduced for the coming breeding season. Talking directly to some trainers/ track managers/owners/blood stock agents would be a good way too.