I don't actually think the concept is a good one (it's unworkable without a level of automation at which you'd have much better alternatives) but the exit problem is already frequently addressed with HOV/bus lanes—have dedicated left-sode exits so they don't need to cross the slower lanes to exit.
I agree advanced automation would be needed to maximize capacity. A basic system only needs cruise control, lights and cameras installed at the merge points and a transponder like fasttrak that monitors your speed and automatically fines you if you hit the brakes.
Adaptive cruise control, lane assist, higher standards of maintenance and driver skill don't seem like too much to ask of a select group of people and vehicles licenced to use the lane and would help to maximize capacity and minimize incidents without getting too futuristic.