Hello.
I’ve been working on a new plugin Harmonic Move.
The plugin will scale an opposite handle to maintain same curvature level when selected handle changes. For example, it can be used to change the weight of terminals:
Am I reinventing the wheel? Is there a better option?
Anyway, feel free to try the plugin. You can get it from GitHub:
Amazing! Fantastic idea and immensely useful, thanks a lot!
Fit Curve? 
Although there are indeed cases when you want different offcurve ratio: my first thought was that’s perfect tool for ‘o’ with a slanted axis, have you tried that?
Also a suggestion: add a shortcut to push handles either way in steps, to make it reusable
As you mentioned, Fit Curve will not help with asymmetric shapes with a different offcurve ratio.
I haven’t tried it with ‘o’ yet, but it looks well-suited for a slanted shapes.
Good idea, thank you for feedback.