This seems really dumb. Essentially what you're doing is creating a small airport off site, where you still have to get there (even earlier) check your bags, go through security, all that shit and then go to the airport on rails. It seems like it would take far longer through this process, not less time. Then you have the security aspect of these vehicles that will be place onto a plane moving through non-secure areas where people could target them.
Then you have all the mechanical issues and complexities that come with this type of system, not to mention the increased weight due to the increased engineering of the aircraft and cabin.
This is 100% pure retardation, a solution to a problem that doesn't exist once again.