I don't see any point in restricting it. They don't restrict buses, nor for that matter do they restrict things like Uber. The only likely time it will hit capacity and see any wait times is at park closing. Otherwise, it doesn't matter if people get on the skyliner to "joyride" as you say. The one downside I see is people choosing to park at CBR and take the skyliner over to a park but we all know that security isn't the best at stopping that.
This isn't to take pressure off the bus system, by the way, that's a nice perk. But let's not forget, they need something unique and good transportation for the Riviera
DVC property. If they don't have something, it's not going to sell at the current price per point no matter how beautiful.