Having an equation editor in the parameter dialogue box would be incredibly useful. The linear style of typing equations is insufficient for accurately entering complex mathematical expressions.
While designing a crank-rocker four bar linkage and specifying the length of its coupler link, I found that correctly sorting out parenthesis errors took nearly as long as deriving the equation for the length of that coupler! Having the ability to type expressions as they might be written by hand (especially for fractions and exponents) would save time, increase clarity, and avoid mistakes for the designer.