What problem does this feature solve?

If the axis labels do not fit, then autoRotate will automatically calculate axisLabel.rotate to make them fit.

axisLabel.interval='auto' will cause missing/skipped labels, like this:

axisLabel.interval=0 will cause collision, like this:

In my opinion, autoRotate will go from 0 to 45 to 90 degrees, depending on the fit, like this:

What does the proposed API look like?

axisLabel.rotate = () => {
  if(this.doesNotFit && this.autoRotate) {
    this.rotate = calcRotateDegrees();
  }
  ...
}