Regarding the title of this post, if this is possible now, I'd love to know, but I don't think it is possible now. It seems like it should've been here from the start. I want to be able to create a button, totally full opacity, and click and something elsewhere on the page fades into view, from zero to full opacity.
I figured out a way to do this a section. Make a button, position it on a page, make it's position fixed and -1 Z index, and then position a section on top of it with a Z index of 0 or 1, with an element inside, such as an image, perhaps positioned on the opposite corner of the section from where the button is. Make the interaction on that section, from zero to full opacity on click. Then, when the user goes to click on that button, they are actually clicking on the invisible section, and the whole thing fades in, making the image fade in.
But this will not work with other kinds of interactions. Any prediction on when interactions will be separated from the element to which the animation is happening?