Timeline extending : We already have a precious function while selecting many clips/layers, which consists in splitting at the play head.
Now what I’d need is being able to extend to the play head if selected tracks/layers allow that.
My example was a group of layers (shape, pattern, text) used as a lower third, that I needed on top during the whole movie. I had to turn the group to a smart object to avoid manually un-trimming the layer.