This capability exists in Excel. . .should also exist in Power BI
What about using parameterized / dynamic scaling where the upper / lower limits and interval step can be set via DAX formula based on measure(s) being plotted against either first or second y-axis?
Another option would be to allow use of parameter slicer where user could select upper/lower limits on vertical axes
A must have for combination charts; i.e., stacked bars on first vertical axis and line on 2nd vertical axis, etc.