[This use to be a long post with multiple broken pictures (if memory serves) so I tried to delete it altogether, but once you have an Idea, Tableau won't let you delete it no matter how bad it is. So in protest I blanked this one (a good one), to show how ridiculous this 'rule' is since it can so easily be circumvented. Now that I've made my point, and because Jonathan complained about me wasting his time, I am restoring this Idea. It doesn't have all the pretty pictures, which doesn't really matter because the devs are going to do it their way anyway.]
Idea: Allow us to create multiple instances of the Measure Names and Measure Values variables so we can assign groups of measures to one axis and a different group of measures to another axis. This would allow us to have a multi-measure line chart laid over a multi-measure bar chart without needing any Custom SQL wizardry.
[This is close enough.]