Are there Bigger Accessible Toilet Stalls in our future?

Yes, maybe, well it depends.  (see, this is the kinda quality response that keeps me in business)

Figure 30a Standard Stall from the 1991 ADAAG

The old ADAAG required that an accessible toilet stall be at least 56″ deep and 60″ wide (the depth increases to 59″ if a floor mounted toilet is used).

This stall is also required to have a 9″ high toe clearance at the front partition and on at least one side.  But if the depth of the stall is increased to 60″, the toe clearance is not required.  See section 4.17.4.

This would permit a 60″ by 60″ stall with walls are partition that extend to the ground.

In the 2004 ADAAG, the minimum dimensions of the stall are the same, but they are more specific with the toe clearance requirement.

First, the toe clearance must extend 6″ minimum under the front partition and one side partition.

Fig. 604.8.1.4 from the 2004 ADAAG

To eliminate the toe clearance at the front partition, the depth must be increased to 62″ with a wall-hung toilet or 65″ with a floor-mounted toilet.

To eliminate the toe clearance at the side partition, the width must be increased to 66″.

Therefore, in order to have a toilet stall/compartment with full height partitions or walls, the minimum dimensions will be 62″-65″ deep and 66″ wide.  See Section 604.8.1.4 Toe Clearance.