That's not to say they don't have some sort of elaborate "mobile attack" plan in place - but their history seems to indicate they are more into long-term planning and surveillance.
I agree with your thoughts on the difficulty involved for such an attack.
They did know when the election was coming. They did know the date of the lunar eclipse. It doesn't matter where the series is played. It does matter that it causes people to gather around the TV set. The series was going to be televised no matter where it was played. Instant audience.
Think mobile. A toy bomb shaped like a football killed four kids in Waziristan about a week ago. How far off can a baseball be?