Effect compositing options: Have a 'layer' option as well as 'mask'
It's be wonderful if, as well as choosing a mask for an effect, we can choose a layer to be used as a mask for an effect; that way, we could use another layer's alpha or luma to control the opacity of the effect, much in the same we we already do with Mask References in the Compositing Options.
Paul, couldn't agree with you more. I will add your vote to the feature request alongside mine. :)