I'ver said before in other threads on this that I would be absolutely 100% in favour of including the monorail in the same way as it is included in The Simpsons: Hit and Run ... a staircase, a short section of broken down track and a discarded locomotive (that you can drive around in, but clearly that wouldn't work in Tapped Out).
Anything else, especially a fully functional monorail, wouldn't really fit with the show itself, especially as we don't really see even the remnants of the monorail in the show now.
As a nod to one of The Simpsons' iconic episodes, and an excuse for another cool skin for Homer, bring it on.
