This is actually a GAC option if the stamp on your card is for a shaded waiting area that is exactly what would happen. Wait to the side while the rest of the party goes through the line, and then meet up with them.
In an ideal world all queues would be wheelchair accessible so all wheelchairs and ECVs would go through the standard line, no questions no cards no fuss. You have a problem standing, rent a wheelchair, you have a bad back, rent a wheelchair. You only need a pass for autism and you bring a doctors note, not unreasonable most people who truly need assistance plan ahead for that. The whole point of GACs is so that guests with disabilities can experience the park the same way as everyone else, not so they can jump in line ahead of everyone else. If a ride offers fastpass then there is no reason why that shouldn't be utilized as is.
I've worked with autistic children a lot and I understand the story that started the thread. The problem is that every Tom ________ and Harry thinks they need the same GAC as an autistic child and those people deserve to abide by the FP system and get them like everyone else. The problem is also that everyone who has a child on the autism spectrum (which everyone falls on somewhere) thinks they need a card. The Autism Society of America says that about 1 million Americans have autism that means .3% of the population, yet a much higher percentage of people each day get a GAC for autism.
I think the system needs to change. Weed out those who just want to get to the front of the line, give assistance to those who really can't navigate the parks without it, have minimal impact on everyone else.
Just a little bit of extra reading:
http://www.usdoj.gov/crt/ada/adahom1.htm
http://www.autism-society.org/site/PageServer