Instead of multiplying the opacities, the checkbox next to the ModelHierarchy node could be used to override the opacity value for its children (as it did before), but this feature is not very obvious.
A toggle button with the two attached icons for this "boss" mode could make it more straightforward.

Currently the checkbox on a parent applies both Color and Opacity to children (though the tip only mentions color, which is a bug).
Do you want control color and opacity separately? Do you have a specific use case when it is needed?

No, I think connecting the models both ways makes sense. However, the set values do not get applied (the display is not updated), only if I hide and show a child model.

Is the checkbox self-explanatory? I created those icons so that the users know what it does.

re-targeted for future

@Csaba - is this something that is really major and high priority for the 4.4 release? If so, would you consider taking it on?

No, this is not high priority. Can be pushed forward. Thanks!

I'm closing this issue as the original problem was that the checkbox did not work, but it does force the parent opacity to the child nodes now, and the feature that was recommended in this ticket is not really necessary, but was proposed as a way to fix the original problem.