I honestly think if this were ever to be feasible you would have to work with systems currently in place. You would be hard pressed to tell intrawest and other resorts to dump the green, blue, black and double black system.
All your ideas are great but they take to much work. I'd rather ride and have the great unexpected thrills of not knowing what is coming next
When dealing with resorts + insurance this should never be allowed. There should never be surprises in that sense. In a regular trail world where insurance doesn't play a role, posting nothing makes sense. But for insurance purposes and encouraging beginners to ride, well advised postings work best. In whistler all trails on the mountain or otherwise are listed with the colour system + the distance and some even have how technical the climb will be (for example forplay is a double black climb and single black descent)...