You are right on this, even Disney has problems with fast pass, and not all big rides have it (very typical the first year of opening on super big rides), becuase they know the only thing they will create is longer waiting times.
There could be a concession done for people that want a fast pass sytem to appear, but it will not impact gamplay (so not fast pass money, no AI behaviour, etc...), only the "theming side". Letting the player add more than one entrance to your ride (this would also come handy for things like multiple drop towers, where the queue is divided in to four but all go to the same ride, etc...).
The only thing guests will do is choose wich one of the entrance has less people, so it usually be 2 euqal smaller queues, as every time the ride opens it will take the same amount of people from each queue.
Ive done a fast drawn example of how it could work:
http://abload.de/img/multiqueuey6bef.png
You can see two examples, a multi queue were all them are normal (typical of drop tower in real life examples) and a coaster queue with a fast pass queue besides it (I know that the real entrance would be bigger than the fast pass one, this was simplified for the example).
So even if the fast pass line wouldnt really have a gameplay purpose, you can build it as a more realisitic theming for your park, and even guests use it. Of course both queues will have aproximately the same number of people in them, because the guest AI will choose were less people are and the proximity of the entrance to decide to use that queue. You can build a longer queue in the normal entrance, so that, as the fast pass one will be shorter and you cant have that many people in that line, they will infact use the normal entrance instead of the "fast pass" themed one.
And still, in the normal multi queue example, it would look like the real thing, with people choosing the queue to enter based in the people in line and the proximity of each entrance in relation to them.
I think that would be a good concession to have something similar to fast pass queues that the guests still will use (so not like the ones some us made in RCT3, that were only there as theming and couldnt be used, as the game didnt support multi queues). At least it will make parks more reallistic without to much work for Frontier.