Currently, when you double-click on a subcomposition node, the subcomposition opens in a new window. This feature request would add an alternative way of opening the subcomposition. When opened this way, the subcomposition would be embedded within the original composition. You would still see the subcomposition node in the context of the original composition, but it would be enlarged / X-rayed so you could also see the contents of the subcomposition.
Unlike Open subcomposition in same window as composition, the original composition surrounding the subcomposition would still be visible, all on one canvas.