First of all, I think the buses hold more than 40 people. Secondly, they run more frequently near park opening. Are you saying that Disney only transports 120 people to Epcot from CBR the hour for rope drop? Lastly, I think the frequency for the cable car will be longer than 30 seconds. We're talking about people with wheelchairs and strollers. No way will they be able to get in and get settled in only 30 seconds.
Walking down Main Street, it's easy to convince ourselves that
ECVs are taking over WDW. But in the grand scheme of things, I don't believe they represent a significant amount of traffic. Using the Disney bus system, my best guess is that we only encounter a
scooter MAYBE 15-20% of the time. Long queues of scooters waiting to board a single bus just isn't a common sight.
The FAQ for the London system claims that it only requires 15 seconds to load each cabin. Strollers will be very easy to drive straight on. ECVs may require some additional delay, but there will be long periods of smooth operations with no scooter loading. They may even build in a system to pre-load scooters and then have the car pop onto the track, similar to ride vehicles at Toy Story Mania.
I worry about the lines that will form early in the morning. I also think there will be a mental thing for people waiting for their turn. A 20 minute wait for the bus is more acceptable than a 20 minute wait in a queue watching other people be whisked away.
The London system runs 10-person cars every 15 seconds. That's a maximum hourly capacity of 2400 passengers. For the sake of argument, let's cut that in half and assume 1200 passengers per hour. (Could easily be higher if Disney installs cabins that accommodate more than 10.) 1200 people is about 20-24 bus loads. Even at rope drop, do your experiences suggest that Disney runs 20 buses per hour between a resort like CBR and Epcot/DHS? That would be a bus arriving every 3 minutes.
Even if running at a modest operating speed, I suspect the passenger throughput would be quite impressive. Much better than buses with the long waits between arrivals and stop-and-go pace along Disney roads. Plus all guests would likely be seated comfortably rather than 50% forced to stand.
And it sounds like buses would continue to run as an alternative.