Here's another question for all you veterans

are walking canes allowed? Because they have walking canes with a pop out seat, just curious if those are allowed in attraction lines or for parades and such.
Walking canes are allowed and people have used the walking canes that have a small seat that folds down from the cane.
Folding chairs or anything that requires more than a second to fold out are not allowed and would not be helpful. As others have mentioned, most lines are slowly moving the whole time you are in them, so there would be no time for folding and unfolding a chair. There would also be no place to keep a chair while the guest is on an attraction.
So, asking to use a folding chair would not be a reasonable accommodation and would also be a safety concern.
WDW makes the recommendation to use a wheelchair or
ECV for situations like this for very good reasons - the distances walked in a day at WDW are very large and unless the guest has a seat with them, in many attractions they will have to stand as part of the experience.
Many attractions involve a preshow or a wait in a 'holding area' for 10-15 minutes or more. Those are often shows that have guests 'collect' in a prehow area while another 'set' of guests is in the show. Once the first guests leave the theater, the doors open for the next set of guests who are waiting in the preshow area.
Having a Guest Assistance Card will not prevent you from standing in those situations. Most of the areas have a very few or no seats at all and you have to wait in the preshow area to get into the show. THe few seats that are available are first come- first served and are not reserved for people with GACs.
Some examples of places where you would have to stand - Guest Assistance Card or not would be:
Studio
Great Movie Ride
American Idol Experience
Sounds Dangerous
Muppet Vision 3D
Voyage of the Little Mermaid
Studio Backlot Walking Tour
Journey Into Narnia
One Man's Dream (This is a walking tour)
Twilight Zone Tower of Terror
Magic Kingdom
Railroad - there is not a preshow, but the train has to come to the station for you to board it.
Tiki Room
Hall of Presidents (currently under renovation)
Haunted Mansion
Country Bear Jamboree
Mickey's Philharmagic
Monster's Inc. Laugh Floor
Stitch's Great Escape
Epcot
Ellen's Energy Adventure
Mission Space
Test Track
Circle of Life (Movie at The Land)
Soarin'
American Adventure
Reflections of China (a 14 minute movie that has no seats, just rails to lean against)
O Canada (a 14 minute move that has no seats, just rails to lean against
Animal Kingdom
It's Tough to Be a Bug
Festival of the Lion King (you will need to wait for the next show)
Wildlife Express Train (you will need to wait for the next train - they leave every 5-7 minutes)
Flights of Wonder (there may not be a place to sit when waiting for the next show)
Finding Nemo (you will be standing during your wait for the next show)