I spent a lot of time looking for script that allows me to select all keyframes from all layers in the current frame in current comp.
The idea is to select keys on all layers, collapsed or not.
It can be script or ui with button.
It will be useful for ae character-animators who need to add keys to hundreds layers at once with one click, without loooooong mouse scrolling.
What i usually do in this situations is select all layers, pressing double "s" to de-collapse all, then U, then drag-drop selection over a very small piece of the timeline. I hope at least this helped.