I could see it being shuttled TM parking. On slow days the rear lot is tight. I think given the choice of using the guest garages or having a shuttle to the back entrance, many TMs would pick the shuttle. Unless you work in park entry, citywalk itself, or Marvel/Suess, it's just not convienent.
And something that occurred to me: if you work Potter, you "can" use the front entrance but it's a loooong walk to go get into your costume and then walk or take the shuttle to your work location. Especially with another Potter being built.