Certainly a good idea, i`ve also put some thought into this few years ago.
After the stage would be generated, you would be allowed to have 2 drives thru it in standard ROAD car and you would create your own pacenotes. Then the 3rd drive would be "real" one, with rally car. And it wouldn`t even be impossible to make this online - just make some queueing system so cars would start with 2 minutes intervals...