it would be a great idea except that if there is alot of bikes on the train it would be hard to get your bike off without whelling it out on one wheel. you would need to have some security like only letting people on that carrage who have a bike so it doesn't get to congested.
they should have the same amount of bike racks as seats, but there would be a problem with tandem bikes.
i don't ride a tandem but i know someone that does and takes it on the train. there is a better way to secure the bikes by hanging the bikes by the front wheel and having a groove to lock the back wheel in place. this would save more space and be easier to get the bike off and on.