Things to consider:
Attractions like Pirates, HM, Splash have show scenes that run on loops. IJA, RSR, the FL dark rides have shows that run on timing. Currently, we don't know how RotR will be and how much of the experience depends on timed show scenes. Shanghai Pirates uses timing because of the screens. This causes the ride vehicles to have to be spaced apart at a minimum distance. How many RotR vehicles they can run depends on that. I'm sure that's something they are continually tweaking. Like Mystic Manor, it may be possible for them to have multiple vehicles in one scene. Again, we don't know.
Also, building footprint size doesn't always equate to ride length proportionally. The northern side of the Pirates building has multiple levels, and the Splash showroom is two levels as well. The FL dark rides are a small footprint, but they twist and turn in corridors which allow there to be more track length. It all depends on how well the current Imagineers designed the space. We have the hanger and AT-AT rooms which are large, but the rest could be a lot winding corridors. Again, we don't know.
We can estimate Falcon because we know roughly how many pods and how many riders in each pod. Capacity will depend on how quickly they can load/unload and how long the ride experience is. Most estimates hit between 1800-2000. For a non-omnimover it's not terrible, but not awesome either. Still more than Star Tours or Splash. I can see RotR being between 2500-3000 if done right, but probably will be closer to 2000-2500. RSR is about 1500 an hour, right? I think it will be a bit better than that.
If you gauge this against Mystic Manor, which is also a trackless system, based on YouTube videos, it looks like the load time (vehicle start to vehicle start) is around 45-50 seconds. It loads 4 vehicles at a time and each holds 6 persons. That makes it about 1700-2000 an hour capacity. RotR holds 8 people. Assuming the same 50 second load time and 4 vehicles loaded at the same time (this is the unknown variable), that puts it at about 2300 an hour. 4 vehicles loaded at a time every 50 seconds allows there to be a 10-12 second spacing between each vehicle, which is plenty of time to reset timed elements in the show.