Since you can set density in the Physics mode of the Mesh Editor, it's only logical that you should be able to set mass as well.

This could be done using parameters, but it would be nice just to be able to do it in the editor itself.

density is related to mass

mass=density * volume

final mass is calculated from the density and object scale.

so it's more logical to set density in the editor, and total mass will be calculated by the engine basing on the object scale