although a max/min angle of motion is able to be specified for RC input, an overall max/min angle cannot be specified for each axis.

For example, if my design allows for a physical -45. +45 range on the roll axis before it hits a physical restriction, it would be great if I could constrain the overall axis to, say 35 degrees.

This way, when the accumulated pitch of the axis became more than 35, it would simply keep it at 35 with respect to the main unit. This would result in higher angles causing the horizon to tilt, but it would not result in reaching the physical limits of the axis (and the resultant knocking/jittering movement which you get when you hit that physical limit).

Perhaps this is not possible without a secondary IMU on the base plane as a reference however ? I’d be interested to know your thoughts anyway.

I'd additionally like to second the request for the ability to use a servo as a yaw control as an option rather than a brushless motor. I think with a gear/pulley drive limiting to say +-30 degrees or so it would be smooth enough for yaw use, and much easier to control than the brushless motor.