What you are proposing calls for the elevator/lift to be on the outside of the ride. It is not possible to get into the cars from that way. There is not enough room for one to come up under the ride to the loading side. Not to mention that the build of that ride makes it difficult to just stop and start easily to load a WC. It sounds like you are not happy with how WDW treats disabled. It's a wonder you go there and support such a horrible company. And this has nothing to do with inclusion. This is more logistics then anything else.
Actually, it does have to with inclusion. I am not saying they are a horrible company, but I am saying if they are serious about inclusiveness, then they need to prove it.
And yes, there is plenty of room to come up underneath.
Here are three possible solutions:
1. Move Lunching Pad elsewhere completely, out in an elevator that you enter from the Tomorrowland side, it would then go up and let out through a door on the opposite side near the exit of the attraction. The wheelchair party can then load directly onto the ride vehicle. This would be the simplest from a logistical standpoint, depending on what exactly is underneath of course, as it would be solely using already existing paths of travel. It could reduce some of the queue space at the end of the speed ramps, so they might have to occasionally adjust how fast they send people up. This is essentially what
Disneyland did, now due to the location of the queue for Rocket Rods, they did utilize a tunnel underneath tomorrowland for the entrance to the elevator, but they wouldn't be necessary here. And by using an elevator with a door on each side (or the can use ones with doors that are 90 degrees from each other if necessary, but those are more difficult to maneuver). The space taken from the load platform could be as damn as about a 40" square, again right at existing paths of travel. I do not fully know the layout of lunching Pad inside, which is why I am saying moving it completely, but it is equally possible that minor modifications would allow for this, but worse case scenario build a new one where some of the tons of unused space is in Tomorrowland.
2. Another option is to build an external elevator not lift and create a bridge that connects to the load platform near the exit speed ramp, again then utilizing existing paths of travel, allowing wheelchair parties to board near where people exit.
3. Modify some of the ride vehicles to allow for loading from the opposite side and create a new platform on the other side for wheelchair parties to load from. This would obviously be quite costly, but would also be doable, albeit full of logistical issues and this would be the least workable in my view.
So, yes, it could be done and fairly easily, but not necessarily cheaply.