"a submerged rail or cable engineered into a purpose built ski lake would be the ticket"
It sure would be "the ticket"... the ticket to total OBSCURITY - and ultimately DEATH of the sport. The boat, boat crew, boating ads, etc, are ALL what make pro tournaments worth watching. If you want to eliminate all those things, just take up cable slalom - I hear it's all the rage in Europe (or something like that).
Also, NOBODY is going to want to spend time with their friends at their place on "a purpose built ski lake" with no boat - how could THEY ever experience the thrill of their first time up on skis? Or just riding on a screaming fast [to them] inner tube? Or riding in the back seat of a 3,000 lb boat doing a 180* turn around at 36 mph?
Lake properties like that would quickly go the way of silent movies - right after our sport did.
As always, IMO.